ABNORMAL TRANSIENT INTERNAL SPHINCTER RELAXATION IN IDIOPATHIC PRURITUS ANI - PHYSIOLOGICAL EVIDENCE FROM AMBULATORY MONITORING

Patients with idiopathic pruritus ani have an abnormal rectoanal inhib itory reflex and a lower threshold for internal sphincter relaxation d uring the saline continence test. This led to the hypothesis that thes e patients may exhibit abnormalities of the transient internal anal sp hincter relaxation reflex. To study this, 23 men of median age 41 (ran ge 27-64) years with idiopathic pruritus ani and 16 male controls of m edian age 39 (range 26-68) years were assessed using computerized ambu latory anorectal electromyography and manometry. Resting anal pressure , maximum anal squeeze pressure, internal sphincter electromyogram fre quency, the number of internal sphincter relaxations and pudendal nerv e terminal motor latency were similar for the two groups. The rise in rectal pressure during internal sphincter relaxation was higher in pat ients with pruritus than in controls (median (range) 29 (18-60) versus 18 (11-37) cmH(2)O, 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) cmH(2)O, P<0.01). The duration of intern al sphincter relaxation was prolonged in patients compared with contro ls (median (range) 29 (18-55) versus 8 (5-12) s, P<0.001). Fourteen pa tients reported staining of underclothes and 17 complained of perianal itch within 1 h of these episodes of abnormal internal sphincter rela xation. Pruritus ani may result from occult faecal leakage as a result of abnormal transient internal sphincter relaxation.