Altered Anal Sensation After Fissure and Surgery: Likely Etiology
The persistent altered anal sensation during sexual activity most likely reflects pudendal nerve dysfunction from chronic straining and/or surgical trauma, rather than the fissure itself or hot-tub exposure. 1, 2
Mechanism of Pudendal Nerve Injury
Chronic straining causes acute pudendal nerve stretch injury that significantly prolongs pudendal nerve terminal motor latency (PNTML) and blunts anal electrosensitivity; these changes correlate with the degree of perineal descent during defecation. 1
Straining for just 1 minute produces measurable pudendal neuropathy that takes 3 minutes to recover in the acute setting, but repetitive strain over time leads to cumulative, potentially permanent sensory deficits. 1
The pudendal nerve is a mixed sensory-motor nerve responsible for anal sensation and sphincter function; stretch injury from perineal descent during straining is the primary mechanism of neuropathic change, not the fissure tissue itself. 1
Why the Fissure Is Not the Primary Cause
Anal fissures are superficial tears in the anoderm that cause pain during defecation but do not directly injure the pudendal nerve, which runs deep in the ischiorectal fossa. 3, 4
The pathophysiology of fissures centers on internal anal sphincter hypertonia and local ischemia, not nerve injury; fissure pain is sharp and localized to bowel movements, whereas altered sensation during sexual activity reflects diffuse sensory dysfunction. 3, 4
Fissure surgery (fistulotomy, sphincterotomy) does not alter pudendal nerve conduction when measured by PNTML in controlled studies, indicating that properly performed anorectal procedures spare the pudendal nerve. 5
Why Hot-Tub Exposure Is Irrelevant
Hot-tub use has no documented mechanism to cause pudendal nerve injury or alter anal sensation; warm water promotes sphincter relaxation (beneficial for fissures) but does not damage neural structures. 3
The guidelines recommend warm sitz baths as adjunctive therapy for fissure healing precisely because heat is safe and non-injurious to pelvic floor nerves. 3, 6
Clinical Evidence Supporting Pudendal Neuropathy
Altered anal sensation during receptive anal intercourse is a recognized consequence of pudendal nerve dysfunction in patients with colorectal disease and pelvic floor disorders; this manifests as decreased sensation, arousal dysfunction, and anodyspareunia (painful anal intercourse). 7
Pudendal nerve injury from chronic straining produces persistent sensory deficits that do not correlate perfectly with motor findings (incontinence), explaining why a patient may have normal continence but altered sexual sensation. 1
In animal models, pudendal nerve transection causes permanent loss of anal sphincter electromyographic activity and decreased anal pressures, demonstrating that nerve injury—not muscle injury alone—drives sensory and motor dysfunction. 2
Surgical Considerations
Lateral internal sphincterotomy (LIS) divides only the internal anal sphincter muscle and does not injure the pudendal nerve when performed correctly; the pudendal nerve runs lateral and deep to the surgical field. 3, 5
However, any major colorectal surgery with extensive pelvic dissection carries risk of pudendal nerve traction injury, particularly if the patient had pre-existing neuropathy from chronic straining. 1, 2
Botulinum toxin injection into the internal anal sphincter is performed under pudendal nerve block in some protocols, confirming that the nerve is accessible to local anesthetic but not typically injured by fissure treatment itself. 8
Diagnostic Algorithm
Obtain pudendal nerve terminal motor latency (PNTML) testing to objectively quantify nerve conduction; prolonged latency (>2.5 ms) confirms neuropathy. 1, 5
Assess for perineal descent during simulated straining; descent >2 cm below the ischial tuberosities strongly correlates with pudendal neuropathy and altered sensation. 1
Rule out atypical fissure etiologies (Crohn's disease, HIV, syphilis, malignancy) if the fissure was off-midline or refractory to standard therapy, as these conditions may independently affect pelvic nerves. 3, 4
Management of Pudendal Neuropathy
Pelvic floor physical therapy with muscle strengthening and stretching is the first-line intervention for pudendal neuropathy affecting sexual function; this addresses sphincter hypertonicity and improves blood flow. 7
Psychological interventions (cognitive-behavioral therapy, sex therapy) help patients adapt to altered sensation and reduce symptom-specific anxiety that exacerbates dysfunction. 7
Avoid further straining by maintaining soft stools with 25–30 g/day fiber supplementation and adequate hydration; this prevents progression of pudendal neuropathy. 3, 6