Internal anal sphincter myopathy causing proctalgia fugax and constipation: further clinical and radiological characterization in a patient.

We report a case of a distinctive familial internal anal sphincter myopathy with unique histological and radiological features. A 67-year-old woman presented with a 20-year history of proctalgia fugax and outlet obstruction; other family members were similarly affected. Computed tomograpy and magnetic resonance imaging demonstrated a grossly hypertrophied internal anal sphincter. Strip myectomy of the sphincter was carried out with improvement in evacuation but little relief of proctalgia. Further relief of symptoms was obtained using oral and transdermal nitrates and a calcium antagonist. Histological examination of the excised muscle revealed hypertrophy and an abnormal arrangement of fibres in whorls; many fibres contained vacuoles with inclusion bodies positive for periodic acid-Schiff. This description of a specific anal sphincter myopathy illustrates the potential importance of histopathological studies of smooth muscle in functional disorders of the gut.