Pathologic features of familial visceral myopathy

Familial visceral myopathy is the most common cause of chronic primary (idiopathic) intestinal pseudo-obstruction. We studied four family groups with this disease and found that it has a characteristic morphologic appearance. Grossly, there is segmental dilatation of the alimentary tract, often involving multiple sites and most commonly producing a megaduodenum. Microscopically, the involved areas show a characteristic change consisting of degenerating muscle cells and fibrosis, which may involve the full thickness of the muscularis propria but is often more prominent in or limited to the external layer. Degenerating muscle cells appear pale, poorly defined, and fragmented. As residual thread-like remnants become surrounded by collagen or as muscle cells are destroyed, leaving apparent spaces surrounded by collagen, the longitudinal and circular muscles take on a vacuolated appearance easily recognized at low magnifications. Recognition of this change is greatly facilitated by use of a trichrome stain, and mild lesions may be recognized only with such stains. The nondilated segments of intestine show similar changes but of a less severe degree. Neural and vascular structures are apparently normal. Although the lesion most closely resembles progressive systemic sclerosis, the degenerating muscle cells and vacuolated appearance of the muscle serve to distinguish familial visceral myopathy from the latter entity.