Abnormal transient internal sphincter relaxation in idiopathic pruritus ani: physiological evidence from ambulatory monitoring.

Patients with idiopathic pruritus ani have an abnormal rectoanal inhibitory reflex and a lower threshold for internal sphincter relaxation during the saline continence test. This led to the hypothesis that these patients may exhibit abnormalities of the transient internal anal sphincter relaxation reflex. To study this, 23 men of median age 41 (range 27-64) years with idiopathic pruritus ani and 16 male controls of median age 39 (range 26-68) years were assessed using computerized ambulatory anorectal electromyography and manometry. Resting anal pressure, maximum anal squeeze pressure, internal sphincter electromyogram frequency, the number of internal sphincter relaxations and pudendal nerve terminal motor latency were similar for the two groups. The rise in rectal pressure during internal sphincter relaxation was higher in patients with pruritus than in controls (median (range) 29 (18-60) versus 18 (11-37) cmH2O, P < 0.01). Furthermore, the fall in anal pressure was greater in patients with pruritus than in controls (median (range) 39 (15-52) versus 29 (21-43) cmH2O, P < 0.01). The duration of internal sphincter relaxation was prolonged in patients compared with controls (median (range) 29 (18-55) versus 8 (5-12) s, P < 0.001). Fourteen patients reported staining of underclothes and 17 complained of perianal itch within 1 h of these episodes of abnormal internal sphincter relaxation. Pruritus ani may result from occult faecal leakage as a result of abnormal transient internal sphincter relaxation.