Charcot-Marie-Tooth Disease with Myelin Protein Zero Mutation Presenting as Painful, Predominant Small-Fiber Neuropathy.

Charcot-Marie-Tooth disease (CMT) rarely presents with painful symptoms, which mainly occur in association with myelin protein zero (MPZ) gene mutations. We aimed to further characterize the features of painful neuropathic phenotypes in MPZ-related CMT. We report on a 58-year-old woman with a longstanding history of intermittent migrant pain and dysesthesias. Examination showed minimal clinical signs of neuropathy along with mild changes upon electroneurographic examination, consistent with an intermediate pattern, and small-fiber loss upon skin biopsy. Genetic testing identified the heterozygous variant p.Trp101Ter in MPZ. We identified another 20 CMT patients in the literature who presented with neuropathic pain as a main feature in association with MPZ mutations, mostly in the extracellular MPZ domain; the majority of these patients showed late onset (14/20), with motor-nerve-conduction velocities predominantly in the intermediate range (12/20). It is hypothesized that some MPZ mutations could manifest with, or predispose to, neuropathic pain. However, the mechanisms linking MPZ mutations and pain-generating nerve changes are unclear, as are the possible role of modifier factors. This peculiar CMT presentation may be diagnostically misleading, as it is suggestive of an acquired pain syndrome rather than of an inherited neuropathy.

Non-length-dependent somatosensory small fiber pathology presenting with restless legs syndrome in pre-motor Parkinson's disease. Evidence from skin biopsy in four patients.

BACKGROUND: The determinants of restless legs syndrome (RLS) occurring in co-morbid association with Parkinson's disease (PD) are currently unknown. METHODS: We performed a skin biopsy in proximal and distal sites of lower limbs in four PD patients, in which RLS had emerged in the pre-motor phase. RESULTS: A reduced somato-sensory intraepidermal nerve fiber (IENF) density mainly in the proximal sites, indicative of non-length-dependent small fiber pathology (SFP), was found in all patients, in absence of electroneurographic signs of large fiber neuropathy. DISCUSSION: The lack of known secondary causes of SFP is consistent with a process intrinsic to PD and, likewise, the absence of known disease conditions associated to RLS, would support the view of a link between the latter disorder and the distal axonopathy. The non-length-dependent pattern of SFP suggest an involvement of the somato-sensory dorsal root ganglia small neurons, consistent with a somato-sensory neuronopathy, which characterizes the RLS in these patients. CONCLUSION: If these findings will be confirmed in a larger cohort of patients, the RLS co-morbid with PD should be regarded as an heterogeneous condition, since the one emerging in the pre-motor phase might represent a prodromal feature of the neurodegenerative disease as an epiphenomenon of somato-sensory SFP. In contrast, for the RLS developing in clinically manifest PD, a possible association with the impairment of the DAergic diencephalo-spinal pathway and the induction by chronic DAergic treatment has been hypothesized.