[Neuropathology of proximal-dominant hereditary motor and sensory neuropathy (HMSN-P)]

Nageotte nodules in human DRG reveal neurodegeneration in painful diabetic neuropathy

Diabetic neuropathy is frequently accompanied by pain and loss of sensation attributed to axonal dieback. We recovered dorsal root ganglia (DRGs) from 90 organ donors, 19 of whom had medical indices for diabetic painful neuropathy (DPN). Nageotte nodules, dead sensory neurons engulfed by non-neuronal cells, were abundant in DPN DRGs and accounted for 25% of all neurons. Peripherin-and Nav1.7-positive dystrophic axons invaded Nageotte nodules, forming small neuroma-like structures. Using histology and spatial sequencing, we demonstrate that Nageotte nodules are mainly composed of satellite glia and non-myelinating Schwann cells that express SPP1 and are intertwined with sprouting sensory axons originating from neighboring neurons. Our findings solve a 100-year mystery of the nature of Nageotte nodules linking these pathological structures to pain and sensory loss in DPN.

Sural nerve pathology in TFG-associated motor neuron disease with sensory neuropathy

The tropomyosin-receptor kinase fused gene (TFG) functions in vesicles formation and egress at the endoplasmic reticulum (ER). A heterozygous missense mutation c.854C > T (p.Pro285Leu) within TFG has been reported as causative for hereditary motor and sensory neuropathy with proximal predominance. Here, we describe two unrelated Chinese pedigrees with 13 affected members harboring the same variant. The clinical, electrophysiological and pathological findings are consistent with motor neuron disease with sensory neuropathy. The main symptoms were painful muscle cramps, slowly progressive proximal predominant weakness, muscle atrophy, fasciculation and distal sensory disturbance. Electromyography revealed widespread denervation and reinnervation. Sural nerve biopsy revealed severe loss of myelinated fibers. Electron microscopy revealed aggregation of ER with enlarged lumen and small vesicles in the remaining myelinated and unmyelinated axons. The mitochondria are smaller in Schwann cells and axons. Some unmyelinated axons showed disappearance of neurofilament and microtubular structures. This is the first report of c.854C > T mutation within TFG in Chinese population. Our findings not only extend the geographical and phenotypic spectrum of TFG-related neurological disorders, but also confirm the abnormalities of ER and mitochondria in sural nerves.