Isoniazid intoxication. Light and electron microscopic findings in muscle and sural nerve biopsies

This study indicates the cellular and ultrastructural changes of the thigh muscle and sural nerve biopsies of a patient intoxicated as a result of isoniazid intake for tuberculosis treatment. The observation of the relative degradation of myelination and fibre type II groups was apparent. The regular concentric layers of the myelin sheath were destroyed. There was a consistent increase in irregular vacuolization and membranous structures in the axon and the cytoplasm of the Schwan cells. It is concluded that poisoning cannot be attributed solely to the axonal degradation but also to the direct toxic effect of the drug.