Peripheral neuropathy in type A Niemann-Pick disease. A morphological study.

A black boy had a severe neuropathic form of Niemann-Pick disease (NPD) with a pronounced sphingomyelinase deficiency in the fibroblasts. Nerve conduction velocities were diminished, and a nerve biopsy was performed. Isolated fibers showed segmental demyelination and numerous dense bodies in the Schwann cells (SC). Electron microscopy revealed two categories of inclusions: the first was made up of lysosomal inclusions usually described in NPD. The second comprised myelin inclusions--sometimes still connected to the original myelin sheath--indicating severe myelinopathy. Both myelin debris and NPD inclusions were found in axoplasms and probably came from SC cytoplasm through axolemma lesions. NPD is a unique example of myelinopathy due to sphingomyelinase deficiency.