The role of muscle biopsy in the diagnosis of neuromuscular diseases

As doenças neuromusculares têm quadro clínico variado e manifestam-se principalmente em pacientes jovens, determinando incapacidade funcional progressiva. Avaliação clínica, eletromiografia, bioquímica sangüínea e biópsia muscular são indispensáveis para o correto diagnóstico etiológico. Apresentamos casuística de 124 casos diagnosticados por biópsia muscular com histoquímica enzimática, microscopia eletrônica e avaliação morfométrica da variação no diâmetro das fibras afetadas, comentando os principais elementos diagnósticos anátomo-patológicos. Necrose muscular, grande variabilidade no diâmetro de fibras e infiltração adiposa muscular predominam nos quadros miopáticos distróficos, que representaram 26% de nossos casos. Redução volumétrica com angulação das fibras sugeriu origem neurogênica, sendo a alteração importante detectada em 27% de nossos diagnósticos. Miopatia mitocondrial caracteriza-se por acúmulos periféricos de grande quantidade de mitocôndrias com ultraestrutura alterada. Cuidados especiais na escolha e coleta da amostra muscular podem minimizar achados inespecíficos ou alterações tipo estádio terminal que impossibilitam a caracterização adequada da doença. Most of the neuromuscular diseases have similar clinical presentation affecting mainly young patients. Clinical observations, serum enzymes, eletromyographic studies and muscle biopsy are required for correct diagnosis. The authors show the results of morphological observations of a series of 124 muscle biopsies studied between 1988 and 1992 using conventional paraffin embedded material, frozen sections of muscle tissue stained by several histochemical techniques, electron microscopic observations and, in some cases, morphometric analysis of the smaller diameter of at least 100 random muscle fibres. Neurogenic atrophy was present in 27% of the cases (n=33), dystrophic muscle was diagnosed in 26%, mitochondrial myopathy in 7% while inflammatory and metabolic myopathies were less frequent. In the group of muscle dystrophy most cases were of Duchenne type showing great variation in fibre size ranging from 10 to 110 microns (mean=30 to 70 microns). There was also muscle necrosis and fatty changes. Neurogenic biopsies showed fibre atrophy with clustering of nuclei and group atrophy. Electron microscopic observations in cases of Werdnig-Hoffmann showed tiny fibres with less than 5 microns in great dimension and also with redundant basal laminae. Cases of mitochondrial myopathy showed the classical ragged red fibres and many different mitochondrial abnormalities under the electron microscope. Many cases (33%) showed only minor structural abnormalities or end-stage alterations with marked fatty infiltration and fibrosis so that a definitive diagnosis failed to be achieved. The correct selection and handling of muscle biopsies is important for adequate diagnosis in neuromuscular pathology.