After a fistulotomy and recent start of diazepam, I feel bladder fullness when standing but not when sitting, and when the bladder is very full the sensation is altered and uncomfortable—what could be causing this and how should I manage it?

Altered Bladder Sensation After Fistulotomy and Diazepam Initiation

Most Likely Diagnosis

Your symptoms—position-dependent bladder sensation (present when standing, diminished when sitting) combined with altered fullness perception after recent fistulotomy and diazepam initiation—most likely represent a combination of pudendal nerve injury from surgery and diazepam-induced detrusor muscle relaxation, rather than incomplete cauda equina syndrome. 1, 2

Immediate Red-Flag Assessment (Within 24 Hours)

You must first rule out incomplete cauda equina syndrome (CESI), which can present with exactly these bladder sensory changes:

• Any new bladder or urethral sensory disturbance after pelvic surgery constitutes incomplete cauda equina syndrome until proven otherwise and mandates emergency lumbar MRI. 1
• Check immediately for bilateral leg radiculopathy, perineal sensory loss beyond the surgical site, progressive leg weakness, or new fecal incontinence. 1
• If any of these neurological signs are present, obtain urgent non-contrast MRI of the lumbosacral spine within 24 hours. 1

If MRI shows cauda equina compression, proceed to emergency neurosurgical decompression within 12 hours—early treatment at the CESI stage prevents permanent bladder dysfunction. 1

If MRI is Normal: Dual Mechanism Explanation

Pudendal Nerve Injury from Fistulotomy

Fistulotomy directly damages pudendal nerve sensory fibers that supply bladder and urethral sensation, explaining your position-dependent symptoms. 1

• The pudendal nerve provides sensory innervation to the perineum, urethra, and contributes to bladder fullness perception. 1
• Position-dependent sensation (better standing, worse sitting) occurs because sitting compresses the already-injured pudendal nerve pathway, further reducing sensory transmission. 3
• Fistulotomy for intersphincteric fistula causes postoperative functional changes in 20% of patients, with sensory alterations being common. 3

Diazepam-Induced Detrusor Relaxation

Diazepam directly inhibits detrusor muscle contractility and increases bladder capacity, which alters your perception of fullness. 2

• Diazepam acts directly on bladder smooth muscle cells by interfering with extracellular calcium influx, reducing detrusor muscle tone and basal contractility. 2
• This pharmacologic effect increases bladder capacity and reduces the intensity of bladder fullness signals, making fullness feel "altered and more uncomfortable" only when the bladder is very distended. 2
• The diazepam effect is unrelated to GABA receptor activation and represents direct smooth muscle inhibition. 2

Management Algorithm

Step 1: Measure Post-Void Residual (PVR) Immediately

Obtain bladder ultrasound or catheterized PVR measurement to assess for urinary retention. 4

• If PVR >250-300 mL: Diazepam must be discontinued immediately, as it is causing clinically significant retention. 4, 2
• If PVR <100 mL: Bladder emptying is adequate despite altered sensation; conservative management is appropriate. 5
• If PVR 100-250 mL: Borderline retention; consider diazepam dose reduction or discontinuation based on indication for benzodiazepine therapy. 4

Step 2: Diazepam Management Decision

Discuss with your prescribing physician whether diazepam can be discontinued or replaced with an alternative that does not affect bladder function. 2, 6

• Diazepam's bladder-relaxing effect is dose-dependent and reversible upon discontinuation. 2
• If diazepam must be continued for essential indication, accept that altered bladder sensation will persist and implement compensated voiding strategies. 2

Step 3: Implement Compensated Voiding Strategy

Use timed voiding every 3-4 hours regardless of perceived bladder fullness to prevent overdistention. 4, 5, 7

• Do not rely on your altered sensation of fullness as a voiding cue—bladder overdistention can cause permanent detrusor damage. 8
• Void in standing position when possible, as this position provides better sensory feedback in your case. 9
• Keep a frequency-volume chart documenting voiding times and volumes to establish your new baseline pattern. 9

Step 4: Monitor for Complications

Reassess PVR in 2-4 weeks after any medication change or if symptoms worsen. 4

• Watch for signs of urinary tract infection (fever, dysuria, cloudy urine), which occurs more frequently with incomplete emptying. 8
• If PVR increases above 300 mL or recurrent UTIs develop, urodynamic studies may be needed to differentiate detrusor underactivity from outlet obstruction. 4

Critical Pitfalls to Avoid

Do NOT start antimuscarinic medications (oxybutynin, tolterodine) for any perceived urgency symptoms—these will worsen your bladder emptying and increase retention risk. 4, 7

Do NOT ignore progressive worsening of sensation or development of bilateral leg symptoms—this would indicate evolving cauda equina syndrome requiring emergency intervention. 1

Do NOT allow bladder overdistention by waiting for "normal" fullness sensation—a single episode of overdistention can cause permanent detrusor muscle damage. 8

Do NOT assume this is purely psychological or will resolve spontaneously—pudendal nerve injury requires 3-6 months for potential recovery, and diazepam effects persist as long as the medication is continued. 1, 2, 3

Expected Recovery Timeline

Pudendal nerve sensory recovery typically occurs over 3-6 months if nerve injury is incomplete. 3

Diazepam-related bladder effects resolve within days to weeks after discontinuation. 2

If sensation does not improve after 6 months and significantly impacts quality of life, formal urodynamic evaluation with electromyography should be performed to guide further management. 4