The pathology of the muscle spindle: A study of biopsy material in various muscular and neuromuscular diseases

Abstract

Changes in the muscle spindle have been studied in 56 muscle biopsies obtained from cases of denervation atrophy (Werdnig-Hoffmann disease, Kugelberg-Welander syndrome, adult motor neurone disease, diabetic neuropathy, chronic peripheral polyneuropathy), progressive muscular dystrophy (Duchenne and limb-girdle types), congenital muscular dystrophy, benign congenital hypotonia and nemaline myopathy, dystrophia myotonica, polymyositis and sarcoidosis, thyrotoxic myopathy, myasthenia gravis and McArdle's disease. In the cases of denervation atrophy a slight thickening of the capsule, an “apparent” enlargement of the periaxial space and an atrophy of the intrafusal fibres, affecting principally the nuclear chain fibres, have been observed frequently. In the cases of progressive muscular dystrophy the most prominent alterations found were thickening of the capsule and of the connective tissue septa inside the spindle, and simple atrophy of the nuclear bag and nuclear chain fibres. Marked “oedematous swelling” of the spindle was noted in 2 cases of limb-girdle dystrophy. There was no exact correlation between pathological changes in the spindle on the one hand and the stage of the disease on the other. In the most severely affected cases of congenital muscular dystrophy there was not only marked atrophy of the intrafusal fibres but these fibres also frequently showed degenerative changes and replacement fibrosis. The capsule of the spindle was often severely thickened. The degree and extent of damage to the intrafusal fibres appeared to be closely related to the stage of the disease. On the whole, the muscle spindle was more frequently and seriously affected in this condition than in progressive muscular dystrophy of the Duchenne and limb-girdle types. In 2 spindles examined in biopsies from cases of dystrophia myotonica moderate atrophy and degeneration of intrafusal fibres was found. In benign congenital hypotonia the intrafusal muscle fibres usually looked normal but their diameter was often reduced if compared with the normal average size of intrafusal fibres in children of appropriate age; furthermore, some spindles contained an unusually large number of intrafusal fibres. The most frequent abnormalities in the spindle in cases of polymyositis were thickening of the capsule and of the connective tissue inside the sheath, an atrophy of the nuclear chain fibres and, occasionally, an “oedematous swelling” of the whole spindle. Somewhat similar changes were observed in a single spindle in a biopsy from a case of sarcoid myopathy. No significant abnormalities have been found in a small number of muscle spindles examined in biopsies from cases of thyrotoxic myopathy and McArdle's disease and in a single autopsied case of myasthenia gravis most of the spindles examined were completely normal, though others showed atrophy and/or degeneration of certain intrafusal fibres.