Neurogenic involvement in distal myopathy (Welander). Histochemical and morphological observations on muscle and nerve biopsies.

Patients with distal myopathy (Welander) were subjected to muscle biopsy from the anterior tibial muscle (n = 4) and to nerve biopsy from the sural nerve at the ankle (n = 5) in order to elucidate a possible neurogenic component of the disease. The type I muscle fibres had a larger mean cross-sectional area as compared to normal controls and an increased variation in fibre size with both hypertrophic and atrophic fibres in one and the same biopsy. A normal muscle fibre type composition was found in the patients. Structural muscle fibre abnormalities such as atrophic fibres, mainly angulated, split fibres, rimmed vacuoles and centrally located nuclei were found in all biopsies. A disorganization and loss of myofibrils as well as autolytic vacuoles were the most prominent findings at the ultrastructural level. Two patients had a moderate loss of myelinated sural nerve fibres. The mean nerve fibre density was decreased as compared to normal controls while the mean nerve fibre area and circular diameter were increased due to selective loss of small diameter (A-delta) nerve fibres. The muscle and nerve fibre abnormalities are discussed with reference to neuropathic and myopathic changes. Some muscle fibre abnormalities are typical for a neurogenic disorder while some others are mostly seen in myopathies but may also appear in neurogenic conditions. A neurogenic etiology in Welander distal myopathy is further supported by the finding of loss of small diameter nerve fibres in the sural nerve.