Bilateral destructive synovitis associated with alpha mannosidase deficiency.

A 13-year-old female with biochemically proven alpha mannosidase deficiency (mannosidosis) developed a bilateral destructive synovitis of the ankle region, a hitherto unreported complication of this disease. Clinically, it was believed to be a pigmented villonodular synovitis. Histologically, the synovium was thrown into villous folds and was infiltrated with clear histiocytes having rare collections of PAS-positive, diastase-resistant material. Electron microscopy demonstrated numerous membrane bound vacuoles filled with granular, amorphous material. This lesion can be distinguished from pigmented villonodular synovitis by its bilaterally symmetrical distribution, the monomorphic population of cells, and the presence of material having the histochemical and ultrastructural properties of (neutral) oligosaccharides.