Detrusor Overactivity: Diary First, Then Urodynamics

Detrusor overactivity is a urodynamic observation: the occurrence of an involuntary detrusor contraction during the filling phase of cystometry, spontaneous or provoked, of variable duration and amplitude (D'Ancona et al., Neurourology and Urodynamics 2019). It is not overactive bladder. OAB is the symptom syndrome that suggests detrusor overactivity clinically; detrusor overactivity is what the trace shows. The difference matters because when the contractions appear on filling, why they appear, and whether the bladder empties afterward all change the next prescription, the next referral, and the next test.

Margaret, 68, retired schoolteacher, sets a paper diary on the desk Tuesday morning. Two failed antimuscarinics behind her: solifenacin 5 mg, then oxybutynin ER 10 mg. Both stopped because she could not remember the names of her grandchildren reliably while on them, and the geriatrician's note in her chart asks whether she should be on any of these medications at all. The chart label is refractory overactive bladder. The diary on the desk says something narrower. Average voided volume of 142 mL across three days. Four sudden urges per day, each within 25 minutes of the prior void. Two leaks per week, none triggered by a cough or a step. The reflexive next move is urodynamics. Maybe. Or maybe the diary already named the mechanism, and the actual next move is a switch to a beta-3 agonist with a 90-day recheck booked before the cystometry slot opens.

What follows is the diary-first, then urodynamics-second, then subtype-stratified prescribing workup for detrusor overactivity. The clinical writing on this topic splits into two camps. The academic camp defines DO precisely and stops at the definition. The patient-education camp conflates DO with OAB and skips cystometry entirely. Neither camp tells a clinician what to do at the visit with Margaret's diary on the desk. The work in this article is the middle: name the mechanism, sort the subtype, decide whether the urodynamics will change management, and match the prescription to what the trace and the diary together actually show.

What detrusor overactivity is, and is not

The International Continence Society defines detrusor overactivity as the occurrence of detrusor contractions during the filling phase of cystometry. The contractions may be spontaneous or provoked, vary in duration and amplitude, and may or may not be perceived or suppressible by the patient (D'Ancona et al., Neurourology and Urodynamics 2019). The definition has two load-bearing words. Cystometry names DO as a urodynamic finding, not a clinical impression. Involuntary names the loss of voluntary inhibition, which is what makes the contraction pathological rather than physiological.

Overactive bladder is a different construct. OAB is a symptom syndrome characterised by urinary urgency, usually accompanied by frequency and nocturia, with or without urgency urinary incontinence, in the absence of urinary tract infection or other detectable pathology (Lightner et al., Journal of Urology 2019). The diagnosis is symptomatic; no instrumented test is required. The two terms collapse into each other in informal use, which causes downstream harm because the treatments, the referral thresholds, and the appropriate workups differ.

The two do not map cleanly. In the Al-Ghazo series of 209 adults referred for cystometric evaluation of OAB symptoms, 76% of male OAB and 59% of female OAB had urodynamically confirmed detrusor overactivity. Urgency urinary incontinence was the strongest single predictor, with odds ratios of 4.2 in men and 2.8 in women on univariate analysis (Al-Ghazo et al., International Neurourology Journal 2011).

The implication for the visit: a symptomatic OAB diagnosis names urgency and frequency, but it does not name detrusor overactivity, and it does not name the four other mechanisms that produce identical-looking symptoms.

The four common mechanisms that present as OAB without detrusor overactivity are sensory urgency without contraction (often interstitial cystitis or hypersensitivity), bladder outlet obstruction with secondary storage symptoms (the BPH pattern that resolves after TURP), polyuria masquerading as frequency (large 24-hour output driving the void count), and detrusor hyperactivity with impaired contractility, the DHIC pattern that is both overactive and underactive in the same bladder. Each calls for a different workup and a different prescription. The conflation of OAB with DO is the source of the failed prescription.

The four subtypes, and why three of them matter at the bedside

The ICS recognises four cystometric patterns of detrusor overactivity: phasic, terminal, compound, and sustained (D'Ancona et al., Neurourology and Urodynamics 2019). Most clinicians know phasic by name and disregard the others. The subtype distinction is clinically actionable.

Phasic detrusor overactivity (PDO) is the characteristic waveform pattern during filling: discrete contractions of variable amplitude and duration, often suppressible, sometimes not. PDO is the textbook DO and the pattern most reliably responsive to first-line pharmacotherapy.

Terminal detrusor overactivity (TDO) is a single involuntary detrusor contraction occurring at or near maximum cystometric capacity, which cannot be suppressed and which often results in incontinence, sometimes with reflex bladder emptying (Gajewski et al., Neurourology and Urodynamics 2018). TDO carries a worse symptom and treatment-response profile than PDO. In the Teji systematic review of 16 studies covering 3,380 patients, TDO patients were significantly older than PDO patients (mean 62.4 vs 49.9 years in one cohort, 63 vs 52 in another), had smaller maximum bladder capacities (385 mL vs 463 mL), and higher peak DO amplitudes (52.6 vs 16.3 cmH₂O). Treatment outcomes diverged accordingly. Following TURP for BPH, PDO patients had a 69.2% success rate; TDO patients had 9.5% (Teji et al., Neurourology and Urodynamics 2025). The subtype, when known, should change the conversation about surgical timing and the post-operative expectation setting.

Compound detrusor overactivity is a series of phasic contractions of progressively increasing amplitude during filling, with each contraction building on the prior baseline. Sustained detrusor overactivity is a prolonged involuntary contraction that does not return to detrusor resting pressure. Both are clinically associated with more severe symptoms and reduced functional capacity, though the dedicated comparative literature is thin (D'Ancona et al., Neurourology and Urodynamics 2019).

The actionable summary: when the urodynamics report lands on the desk, read the subtype, not just the presence or absence of DO. The same drug at the same dose has different odds of working in PDO versus TDO. Wang and Kuo demonstrated this directly in a real-world cohort of 453 OAB patients with urodynamic DO. Phasic DO patients reached 50.7% overall success on first-line OAB medication; terminal DO patients reached 42.0%. Patients receiving mirabegron alone had a significantly higher initial medication success rate than those on solifenacin or combination therapy (Wang and Kuo, Tzu Chi Medical Journal 2022). For the older patient with TDO, the cumulative literature supports beta-3 first, not antimuscarinic first. Margaret in the opening case sits inside this argument from a different direction. Her diary signatures (small AVV, urge clustering within minutes of prior voids, scattered UUI) point at phasic DO, not terminal. But the prescribing constraint is the same: two failed antimuscarinics, documented cognitive side effects, an active geriatrician on the chart. The right next prescription is mirabegron, not a third antimuscarinic.

Aetiology, in three buckets

Detrusor overactivity is classified by underlying cause as idiopathic, neurogenic, or non-neurogenic (secondary) (D'Ancona et al., Neurourology and Urodynamics 2019).

Idiopathic detrusor overactivity has no identifiable provoking factor. It is the majority. The mechanism is dual: a myogenic theory of partial detrusor denervation producing increased excitability of remaining smooth muscle, and a neurogenic theory of loss of supraspinal inhibition from the pontine micturition centre and periaqueductal grey. The two are not mutually exclusive, and most cases probably involve both (Foon and Toozs-Hobson, Obstetrics, Gynaecology and Reproductive Medicine 2007).

Neurogenic detrusor overactivity (NDO) requires a relevant neurological disorder: multiple sclerosis, spinal cord injury, stroke, Parkinson's disease, spina bifida, or central or peripheral nerve disease relevant to the lower urinary tract. NDO is common in the populations it affects. Approximately 50% of MS patients report urinary incontinence over the course of the disease, and most SCI patients develop some bladder dysfunction (Drake et al., Neurourology and Urodynamics 2014).

The clinical priority in NDO is upper-tract protection, not symptom relief. Detrusor leak point pressures above 40 cmH₂O are the classic threshold above which upper-tract risk rises in neurogenic bladders, and the threshold that drives the treatment intensity decision (Lane et al., Neurourology and Urodynamics 2018).

Non-neurogenic secondary DO is the third bucket. The classic example is the man with bladder outlet obstruction from BPH whose detrusor has remodelled in response to chronic outflow resistance and whose storage symptoms resolve after the obstruction is relieved. The under-recognised version is post-surgical DO, with a de novo DO rate of approximately 10.8% reported after bladder-neck surgery (Foon and Toozs-Hobson, Obstetrics, Gynaecology and Reproductive Medicine 2007). Treating the storage symptoms in a man with documented obstruction as primary OAB before addressing the obstruction is a category error. The storage symptoms are the obstruction's downstream effect, and they often resolve when the obstruction does. A fourth pattern (DHIC) sits across these buckets and is the subject of the next section.

DHIC, the overactive-and-underactive bladder

Detrusor hyperactivity with impaired contractility (DHIC), sometimes described as the coexisting overactive-underactive bladder syndrome (COUB), is the pattern in which the same detrusor produces involuntary contractions during the filling phase while failing to produce an effective contraction during the voiding phase (Finazzi Agrò, IUGA Spotlight 17(5)). The two findings look paradoxical until the time axis is added: overactivity is a filling-phase observation, underactivity is a voiding-phase observation, and the same muscle can exhibit both within the same cycle.

DHIC is common in elderly bladders, post-stroke bladders, and neurogenic populations. The prevalence among MS patients with voiding difficulty approaches 50% (Finazzi Agrò, IUGA Spotlight 17(5)).

The proposed mechanisms include bladder wall ischaemia, partial denervation, and long-standing bladder outlet obstruction producing both reactive overactivity during filling and exhaustion during voiding.

The clinical consequence of DHIC is that the standard first-line OAB prescription harms rather than helps. Antimuscarinics, which suppress the involuntary filling-phase contractions, also impair the already-weak voiding-phase contraction. The result is rising post-void residual, increased UTI risk, and in the worst case acute urinary retention. The safer prescribing pathway for suspected DHIC is a beta-3 agonist (mirabegron, vibegron), which targets the storage-phase overactivity through detrusor relaxation without compromising the voiding-phase contraction. Neuromodulation, particularly sacral nerve stimulation or posterior tibial nerve stimulation, is the attractive third-line because both modalities address both ends of the dysfunction (Finazzi Agrò, IUGA Spotlight 17(5)).

The detection of DHIC pre-urodynamics rests on the diary plus the PVR. A patient with diary signatures of storage impairment (small voided volumes, urgency clusters, urge incontinence) and voiding impairment (double-void notation, PVR over 100 mL, voiding efficiency under 70%) is a presumptive DHIC until the cystometry confirms or refutes. The full workup is covered in the underactive bladder diary-first article and the post-void residual workup.

How OAB symptoms predict DO, imperfectly and with a sex difference

The Al-Ghazo cohort is the cleanest data source on the symptom-to-finding mapping. In their 209-patient series, the overall DO incidence among OAB symptom presenters was 76.1% in men and 58.7% in women. The OAB-wet subset performed better as a predictor than OAB-dry: 93% of men and 69.8% of women with urgency plus urgency urinary incontinence had confirmed DO, against 63% of men and 61% of women with urgency alone (Al-Ghazo et al., International Neurourology Journal 2011).

The symptom-level predictors carry a sex difference. In men, the multivariate model retained urgency and UUI as the significant predictors of DO. In women, the model retained nocturia and UUI. Frequency alone was a poor predictor in both sexes. Urgency alone was a significant predictor in men but not in women. The interaction terms matter more than the single-symptom odds ratios. The combination of urgency plus UUI raised the OR for DO from 4.2 to 6.8 in men; the combination of nocturia plus UUI produced an OR of 3.3 in women (Al-Ghazo et al., International Neurourology Journal 2011).

The deeper framing is Blaivas's: the bladder is an unreliable witness (Blaivas, Neurourology and Urodynamics 1996). The same symptom set can arise from detrusor overactivity, sensory urgency without contraction, polyuria, BOO-induced storage symptoms, infection, interstitial cystitis, or pelvic-floor dysfunction. The symptom complex narrows the differential; it does not name the diagnosis. The instrumented finding is what does that, and the instrumented finding only matters if it changes the next decision.

The bladder diary as pre-urodynamics triage

The diary is the cheapest, fastest, lowest-burden filter on whether the cystometry is needed at all. Four diary patterns flag detrusor overactivity ahead of the trace, and a fifth pattern rules it out.

Pattern one: small average voided volume with normal 24-hour output. Average voided volume under 200 mL against a 24-hour output in the 1.5 to 2.5 litre target range points at reduced functional capacity, which is the signature of phasic DO or terminal DO with reflex emptying. The patient is not over-producing; the bladder is not holding. Pair this with the frequency volume chart read.

Pattern two: urgency clustering within 30 minutes of prior voids. When the diary documents sudden urge episodes within 15 to 30 minutes of a recently completed void, the pattern is consistent with poor cortical inhibition between contractions, which is the bedside signature of phasic DO. Compare with the patient whose urges build over 60 to 90 minutes; that is sensory urgency, not detrusor overactivity.

Pattern three: scattered urge incontinence episodes without postural triggers. UUI events distributed through the day, none associated with cough, sneeze, lift, laugh, or postural change, indicate an urge mechanism rather than a stress mechanism. Combined with patterns one and two, this is a presumptive DO that the prescription can address without UDS.

Pattern four: terminal urge pattern. A small number of large-volume urge events, often near maximum cystometric capacity, with reflex emptying or near-complete leakage, points at terminal DO specifically. These patients are older on average, have smaller capacity, and respond worse to standard first-line antimuscarinics (Teji et al., Neurourology and Urodynamics 2025). The diary itself is a referral indication.

Pattern five: the polyuria masquerade. Large average voided volume (400 mL or more) with high 24-hour total (>2.5 litre) and elevated nocturnal polyuria index reroutes the workup away from DO and toward the differential diagnosis of polyuria. The frequency is real; the mechanism is output, not bladder dysfunction. Treating this pattern as OAB produces the failed prescription.

The full diary read is covered in the bladder diary interpretation walkthrough. The point is that a 3-day diary, read with the four-pattern framework, answers most of what cystometry would and identifies the patients for whom cystometry is the next correct step.

When to order urodynamics

The AUA/SUFU 2019 guideline position is unambiguous: cystometry, postvoid residual testing, urodynamic study, cystoscopy, and bladder ultrasonography are not necessary in the initial workup of uncomplicated overactive bladder. They are reserved for refractory cases or otherwise complicated presentations (Lightner et al., Journal of Urology 2019). The 2026 EAU male LUTS guidelines were updated this year with revised diagnostic and treatment recommendations that align broadly with the AUA position on UDS as a second-line tool rather than a first-line workup (Baboudjian et al., European Urology 2026).

The indications that change the calculus, and that make the cystometry slot worth the wait, are:

1. Refractory to two adequate trials of first-line agents from different classes (antimuscarinic and beta-3 agonist), each at therapeutic dose for at least 8 to 12 weeks.
2. Suspected neurogenic detrusor overactivity with documented or suspected MS, SCI, stroke, Parkinson's, spinal stenosis, or relevant central nervous system pathology. The upper-tract protection imperative makes the storage pressure measurement non-optional.
3. Persistent storage symptoms after BPH-directed surgery. Pre-operative TDO is a documented risk factor for post-TURP storage-symptom persistence (Teji et al., Neurourology and Urodynamics 2025). When the storage picture persists at 6 to 12 weeks post-surgery, urodynamics distinguishes residual obstruction from primary DO from DHIC.
4. Suspected DHIC, as flagged by diary signatures of combined storage and voiding impairment plus PVR over 100 mL. The pressure-flow study confirms the dual finding and informs the prescribing pivot.
5. Before any third-line invasive therapy (intradetrusor onabotulinumtoxinA, sacral neuromodulation). Confirmation of the diagnosis precedes the device or the injection.
6. Mixed urinary incontinence with unclear dominance, particularly in women where stress and urge components coexist and the surgical sling decision depends on the contribution of each.
7. Hematuria, recurrent UTI, prior pelvic radiation, prior pelvic surgery, or other red-flag findings that demand structural workup as part of the differential.

The framing that matters: urodynamics is informative when the result will change the next prescription, the next procedure, or the next referral. When the diary, the symptom pattern, and the response to two first-line trials already point at a treatment direction, the cystometry adds expense and patient burden without changing the management. Order it when the result will move the workflow. The cystometry slots I most regret booking are the ones that confirmed what the diary already said. The slots I most regret skipping are the ones where a missed DHIC sent a patient into retention on the antimuscarinic I prescribed for the OAB label they arrived with.

What detrusor overactivity looks like on the trace

The pressure-flow tracing displays three pressures simultaneously: vesical pressure (Pves) measured by the intravesical catheter, abdominal pressure (Pabd) measured by the rectal catheter, and detrusor pressure (Pdet), which is the calculated difference (Pdet = Pves − Pabd). The Pdet trace is the one that shows detrusor overactivity.

The phasic DO waveform is a discrete upstroke on the Pdet trace during the filling phase, of variable amplitude (typically 15 to 40 cmH₂O in idiopathic DO, often higher in neurogenic DO), with or without an accompanying urge sensation reported by the patient. The contraction may resolve spontaneously or persist; the patient may suppress it or not. The signature is the Pdet rise on a Pabd-stable background.

The terminal DO waveform is morphologically distinct. It is a single involuntary contraction at or near maximum cystometric capacity, with the Pdet rising sharply, the patient unable to suppress, and the contraction terminating in reflex bladder emptying or substantial incontinence. The peak amplitude is often substantially higher than in PDO; the Cubuk series reported mean peak amplitudes of 52.6 cmH₂O in TDO against 16.3 in PDO (Teji et al., Neurourology and Urodynamics 2025).

The artifact most often mistaken for DO is the abdominal pressure spike that elevates Pves without elevating Pdet. When a patient coughs, strains, or shifts position, Pves and Pabd rise together; the calculated Pdet stays flat. The cough test, performed at intervals throughout the cystometry per the ICS Good Urodynamic Practices protocol, confirms the integrity of the pressure subtraction and rules out artifact (Schäfer et al., Neurourology and Urodynamics 2002). When the report shows DO without documented cough testing, the finding warrants a second read.

The clinical bedside translation: a Pdet rise on a stable Pabd background during filling, accompanied by a reported urge sensation, is detrusor overactivity. A Pves rise with a matching Pabd rise is abdominal artifact. The subtype is named by the contraction's timing within the filling phase. The trace's job is to confirm or refute the diary's hypothesis, and the trace earns its keep when the hypothesis was specific enough to test.

First-line treatment, with subtype and patient considerations

The AUA/SUFU treatment ladder for non-neurogenic detrusor overactivity progresses from behavioural therapy through first-line pharmacotherapy to third-line invasive options (Lightner et al., Journal of Urology 2019). The behavioural foundation is bladder training, fluid manipulation, urge-suppression technique, and pelvic-floor coordination. These remain underused in primary care and over-skipped in specialist practice; the response rates rival pharmacotherapy at zero side-effect cost when the patient engages with the protocol.

First-line pharmacotherapy is antimuscarinic monotherapy, beta-3 agonist monotherapy, or combination. The class choice is patient-specific.

Antimuscarinics (oxybutynin immediate-release and extended-release, tolterodine, solifenacin, darifenacin, trospium, fesoterodine) act through M3 muscarinic receptor blockade on the detrusor smooth muscle. Efficacy is comparable across the class. Side-effect burden is dose-dependent and includes dry mouth, constipation, blurred vision, urinary retention risk, and central nervous system effects (sedation, cognitive impairment). The cognitive concern is the load-bearing one for older patients. Long-term anticholinergic exposure has been associated with elevated dementia incidence in two large cohort studies, with the strongest signal in the older long-duration users; the Coupland series specifically documented a dementia AOR of 1.65 for bladder antimuscarinic exposure above 1095 TSDDs (Coupland et al., JAMA Internal Medicine 2019; Gray et al., JAMA Internal Medicine 2015). The clinical recalibration is that antimuscarinics are reasonable first-line in younger patients without cognitive comorbidity, and beta-3 first in patients over 70, in patients with mild cognitive impairment, in patients with concurrent anticholinergic load from other medications, and in suspected DHIC.

Beta-3 agonists (mirabegron, vibegron) relax the detrusor through beta-3 adrenoceptor activation during the storage phase. The efficacy is comparable to antimuscarinics. The tolerability is better. The blood pressure monitoring caveat applies, with periodic BP checks recommended particularly in the first 3 months. The mechanism is permissive for DHIC because it does not impair the voiding-phase contraction. The Wang real-world cohort showed mirabegron monotherapy outperforming both solifenacin monotherapy and combination therapy as the initial-medication choice, supporting beta-3 first when the patient is older, when DHIC is suspected, or when the urodynamic subtype is terminal DO (Wang and Kuo, Tzu Chi Medical Journal 2022).

Combination therapy (antimuscarinic plus beta-3) is supported by the BESIDE trial data showing additive efficacy over monotherapy in patients with partial response to either agent alone (Drake et al., European Urology 2016). The combination carries the combined side-effect profile; it is appropriate for the partial responder, not the first-line attempt.

The subtype-stratified summary: phasic DO responds well to either class as monotherapy or to combination. Terminal DO responds better to mirabegron monotherapy than to solifenacin monotherapy. DHIC patterns favour mirabegron over any antimuscarinic. Neurogenic DO often requires combination at higher doses, with onabotulinumtoxinA as the third-line standard at 200 U rather than the non-neurogenic 100 U.

Third-line therapy, when first-line fails

Refractory detrusor overactivity, defined as inadequate response after 8 to 12 weeks each of two first-line agents from different classes, opens the third-line options.

Intradetrusor onabotulinumtoxinA at 100 U for non-neurogenic DO and 200 U for neurogenic DO is administered by cystoscopic injection across multiple bladder wall sites, sparing the trigone. The mechanism is presynaptic blockade of acetylcholine release at the neuromuscular junction. The duration of effect is 6 to 9 months typically. The procedural prerequisites include patient willingness to perform clean intermittent catheterisation if urinary retention develops post-injection, and post-procedure PVR monitoring at intervals consistent with the institutional protocol. The Ke series reported 84% symptom improvement on PPBC scores in PDO patients versus 73% in TDO patients (Teji et al., Neurourology and Urodynamics 2025). The subtype influences the response rate; it does not contraindicate the procedure in either group.

Percutaneous tibial nerve stimulation (PTNS) is delivered as 30-minute sessions weekly for 12 weeks, then tapered to monthly maintenance. The mechanism is afferent neuromodulation through the S2-S4 sacral plexus via the posterior tibial nerve. The treatment is non-invasive, low-burden in the office, and well-tolerated. The relapse rate after stopping maintenance is the main limitation. In the van der Pal cohort of successfully-treated PTNS patients, 7 of 11 (64%) experienced a ≥50% increase in incontinence episodes or voiding frequency within 6 weeks of stopping maintenance, with significant deterioration in mean voided volume, nocturia, and incontinence severity (van der Pal et al., BJU International 2006). The patient candidate profile favours those willing to commit to weekly visits initially and monthly maintenance long-term.

Sacral neuromodulation (SNS, InterStim) is the more invasive third-line option, with a staged trial period using a percutaneous lead followed by full implantation in responders. The mechanism is direct modulation of the S3 nerve root afferent and efferent traffic. SNS is the preferred third-line for DHIC because it addresses both storage overactivity and voiding underactivity through the same intervention. The procedure carries surgical risks including infection, lead migration, and the need for reoperation in approximately one-third of patients over follow-up. In the Peters single-institution series of 407 SNS patients, 134 (33%) required at least one reoperation over a median follow-up of 28.9 months, with 19% undergoing revision and 14% explantation; the most common reason was lack of efficacy or worsening symptoms (Peters et al., Neurourology and Urodynamics 2017).

Reconstructive options (augmentation cystoplasty, urinary diversion) are last-resort interventions reserved for failed third-line therapy with documented upper-tract risk or unmanageable incontinence. They are not part of the standard non-neurogenic DO pathway.

Special populations

Geriatric detrusor overactivity carries the anticholinergic-burden concern as the load-bearing prescribing constraint. The accumulating evidence linking long-term anticholinergic exposure to dementia incidence has shifted prescribing toward beta-3 first in patients over 70, particularly when the patient already carries anticholinergic load from antihistamines, tricyclic antidepressants, antispasmodics, or muscle relaxants (Coupland et al., JAMA Internal Medicine 2019; Gray et al., JAMA Internal Medicine 2015). Margaret in the opening case is exactly this profile: a 68-year-old who came off two antimuscarinics for cognitive side effects she could feel and her geriatrician could see. The deprescribing conversation, when a long-standing antimuscarinic was started years prior, deserves the same care as the initial prescribing decision. A baseline cognitive screen (MMSE, MoCA) before initiation or continuation is reasonable practice in patients over 75 or with subjective cognitive complaints.

Neurogenic detrusor overactivity requires a different treatment hierarchy. Upper-tract protection takes precedence over symptom relief. Storage pressures above 40 cmH₂O at clinically relevant volumes drive treatment intensification regardless of symptom severity. Combination first-line pharmacotherapy is more common. Intradetrusor onabotulinumtoxinA at 200 U is the established third-line (Drake et al., Neurourology and Urodynamics 2014). Clean intermittent catheterisation is often part of the management from earlier in the pathway, not held in reserve.

Post-prostatectomy and post-TURP persistent detrusor overactivity is the under-recognised pattern. Pre-operative TDO predicts post-operative storage-symptom persistence, with the Teji review documenting the 9.5% PDO-versus-TDO TURP success disparity (Teji et al., Neurourology and Urodynamics 2025). The implication for the BPH workup is that the pre-operative urodynamic finding is informative when the patient has terminal-pattern symptoms or diary signatures suggestive of TDO. Post-operatively, the persistent storage picture warrants medication-class re-evaluation, with mirabegron often the better choice than the antimuscarinic the patient was started on before surgery.

When detrusor overactivity is not what you think

The differential for OAB-pattern symptoms in the absence of confirmed detrusor overactivity:

| Differential | Distinguishing feature | Workup | |---|---|---| | Sensory urgency without contraction | Urge at low volumes, no Pdet rise on cystometry | Cystometry, cystoscopy if pain or hematuria | | Interstitial cystitis / bladder pain syndrome | Pelvic pain with urgency, low functional capacity | Bladder pain history, cystoscopy with hydrodistension if indicated | | Polyuria | High 24-hour output (>2.5 L), large voided volumes | Differential diagnosis of polyuria | | Nocturnal polyuria | Elevated NPi (>33% in older adults, >20% in younger) | Nocturnal polyuria index | | Urinary tract infection | Recent onset, dysuria, abnormal urinalysis | Urine culture, treat the infection | | BPH with secondary storage symptoms | Concurrent voiding symptoms, elevated PSA, enlarged prostate | Uroflow, PVR, IPSS, structural workup | | Pelvic-floor dysfunction | Coordination signs on exam, response to PT | Pelvic-floor PT assessment | | Functional / behavioural frequency | High frequency, normal volumes, no UUI | Diary review, behavioural reassessment |

The diagnostic discipline that anchors the differential is the diary read first, the symptom cluster mapped to the IPC 4Is functional buckets second, the targeted instrumentation third. The cystometry is the gold standard for confirming detrusor overactivity, but the cystometry is not the start of the workup. It is the test that earns its place after the diary, the symptom cluster, and the response to two first-line trials have already narrowed the differential to the one or two mechanisms the test can adjudicate.

FAQ

What is detrusor overactivity? Detrusor overactivity is a urodynamic observation: an involuntary detrusor contraction during the filling phase of cystometry, spontaneous or provoked, of variable duration and amplitude. It is not the same as overactive bladder, which is a symptom syndrome diagnosed clinically.

What is the difference between overactive bladder and detrusor overactivity? OAB is a symptom syndrome characterised by urgency, usually with frequency and nocturia, with or without urgency urinary incontinence. Detrusor overactivity is the cystometric finding of an involuntary detrusor contraction during filling. The two overlap, but imperfectly: approximately 76% of male OAB and 59% of female OAB present with urodynamically confirmed DO, and the strongest predictor in both sexes is urgency urinary incontinence.

What causes detrusor overactivity? The aetiology is classified as idiopathic (the majority, with dual myogenic and neurogenic mechanisms), neurogenic (multiple sclerosis, spinal cord injury, stroke, Parkinson's, spina bifida), or non-neurogenic secondary (typically bladder outlet obstruction from BPH, also post-surgical). The fourth common pattern is detrusor hyperactivity with impaired contractility (DHIC), in which the same detrusor is overactive during filling and underactive during voiding.

What is the ICD-10 code for detrusor overactivity? Detrusor overactivity does not have a dedicated ICD-10 code. The code selection depends on the clinical picture: N32.81 for overactive bladder syndrome, N39.41 for urge urinary incontinence with documented leakage, N31.1 for reflex neurogenic bladder when neurogenic aetiology is documented. The full coding walkthrough is in ICD-10 codes for urinary urgency.

What is the difference between phasic and terminal detrusor overactivity? Phasic DO is the characteristic waveform pattern of discrete involuntary contractions during filling, often suppressible. Terminal DO is a single involuntary contraction occurring at or near maximum cystometric capacity, unsuppressible, often with reflex bladder emptying. TDO patients are older on average, have smaller bladder capacity, and respond worse to most first-line treatments. The subtype, when known, should inform the prescription and the surgical timing conversation.

How is detrusor overactivity treated? The treatment ladder is behavioural therapy (bladder training, fluid manipulation, urge suppression, pelvic-floor coordination) first, then first-line pharmacotherapy (antimuscarinic monotherapy, beta-3 agonist monotherapy, or combination), then third-line options (intradetrusor onabotulinumtoxinA, percutaneous tibial nerve stimulation, sacral neuromodulation), and reconstructive surgery as last resort. The class choice within first-line is patient-specific, with beta-3 preferred for older patients, suspected DHIC, and terminal DO subtype.

Do I need urodynamics to diagnose detrusor overactivity? The AUA/SUFU 2019 position is that urodynamics is not required for uncomplicated OAB. The indications that change the calculus include refractory symptoms after two first-line trials, suspected neurogenic aetiology, persistent storage symptoms after BPH surgery, suspected DHIC, and before any third-line invasive therapy. The diary plus PVR plus symptom cluster carries most of the diagnostic weight in the first-line workup.

What happens if detrusor overactivity is left untreated? The quality-of-life trajectory is progressive in most idiopathic cases, with documented effects on social functioning, sleep quality, work productivity, and psychological wellbeing. In neurogenic DO with elevated storage pressures, the upper urinary tract is at risk of hydronephrosis and renal function decline. In elderly patients, the nocturia and urge incontinence components increase fall risk. The untreated trajectory is rarely benign.

Is mirabegron better than antimuscarinics for detrusor overactivity? Efficacy is comparable across the two classes in non-neurogenic DO. Tolerability favours beta-3 agonists, particularly in older patients and those with cognitive risk or anticholinergic load from concurrent medications. The Wang 2022 real-world data showed mirabegron monotherapy with the highest initial success rate among the first-line options, particularly relevant to patients with terminal DO and to elderly patients where anticholinergic burden is the constraining concern. The cumulative case for beta-3 first has strengthened over the past decade, particularly in geriatric DO.

What is detrusor hyperactivity with impaired contractility (DHIC)? DHIC, also called the coexisting overactive-underactive bladder syndrome (COUB), is the pattern in which the same detrusor exhibits involuntary contractions during filling and impaired contractility during voiding. It is common in elderly bladders, post-stroke bladders, and MS bladders (up to 50% of MS patients with voiding difficulty). Antimuscarinics carry retention risk in DHIC; mirabegron and neuromodulation are the safer treatment pathways.

Where to go from here

Open the bladder diary calculator: bladderdiaries.com/entry

Two ways in: upload a digital diary PDF (from myflowcheck.com or any structured export), or enter the data manually. The calculator returns 24-hour voided volume, NPi, MVV, AVV, voiding efficiency, and the IPC 4Is mapping in seconds. The diary patterns that flag detrusor overactivity (small AVV, urgency clustering, scattered UUI, terminal-urge events) surface in the read.

For the workup adjacent to detrusor overactivity, the bladder diary interpretation walkthrough covers the full read-through procedure. Frequency volume chart interpretation covers the voided-volume distribution analysis. Post-void residual covers the PVR thresholds that confirm or refute DHIC. Underactive bladder covers the contractility-failure pattern that pairs with DHIC. ICIQ-OAB item-by-item interpretation covers the symptom questionnaire that pairs with the diary. ICD-10 codes for urinary urgency covers the coding decisions for the DO clinical pictures. Nocturnal polyuria index and differential diagnosis of polyuria cover the masquerade patterns that should not be treated as DO.

Author: Dr. Di Wu, MD, PT (IPC founding member). Medically reviewed by Dr. Steven Tijerina, PT, DPT, Cert. MDT (IPC US Director). Photo: Bozhin Karaivanov on Unsplash.