The pathology of the muscle spindle in myasthenia gravis.

Abnormalities in the morphology and motor innervation of the muscle spindles are described in 4 autopsied cases of myasthenia gravis. There were changes consistent with motor denervation in 5 of 118 spindles examined in sectioned material. In 65 teased, silver-impregnated spindles there was proliferation of the fusimotor innervation due to axonal sprouting occurring in the endings themselves. Motor end-plates on the intrafusal muscle fibres showed "dystrophic" changes similar to those previously described in extrafusal muscle in this disease. The sensory innervation was normal. The possible signifance of these findings is discussed.