Immunofluorescence on skeletal muscle and skin biopsy specimens in muscle diseases.

A series of 110 muscle and 40 skin biopsy specimens were examined using direct immunofluorescence aiming to identify features that may differentiate the myopathy of connective tissue disease from other muscle diseases. The skeletal muscle fluorescence was positive in 75% of the patients with muscle diseases. The sarcolemmal staining was higher in mitochondrial encephalomyopathy. Fiber and vascular staining occurred in all muscle diseases, except in cases of myasthenia. Our results showed that 42% of patients with polymyositis and 43% of patients with peripheral motor neuron diseases have vascular deposits of immune complexes suggesting that these two diseases could result from an immune-complex-induced vasculopathy. The IF test in skin specimens was positive in 60% of the patients with muscular diseases. The absence of immunoglobulin deposit at the dermoepidermal junction and at epidermal nuclei in cases of peripheral motor neuron disease suggest that this skin test may be useful in the differentiation of muscle diseases.