Intranuclear and cytoplasmic filamentous inclusions in distal myopathy (Welander).

Ultrastructural examination of anterior tibial muscle from four patients with late-onset autosomal dominant distal myopathy of Welander-type revealed intrasarcoplasmic filamentous inclusions in association with rimmed vacuoles. In one of the patients, identical intranuclear filamentous inclusions were also found. These filamentous inclusions are similar to those described in inclusion body myositis (IBM). They have also been observed in hereditary neuromuscular disorders including autosomal recessive distal myopathy. Thus, the filamentous inclusions occur in different neuromuscular conditions with different etiologies. These findings further raise the question of the specificity of the filamentous inclusions in IBM.