Ultrasound and Electromyography Findings in Charcot-marie-tooth Disease Type 4J: A Rare Case Study

Case Diagnosis: Charcot-Marie-Tooth (CMT) disease 4J with electrodiagnostic features of acquired demyelination.

Case Description: This patient was referred to the electrodiagnostic lab with >6 months of progressive pain in the medial thigh, calf, and back without any reported weakness, numbness, or tingling. No upper limb sensory symptoms, cranial nerve, or bowel/bladder dysfunction were noted. Exam revealed a loss of proprioception distally, diminished reflexes throughout, and normal pinprick. Strength was normal throughout besides 4/5 hallux extension. Nerve conduction studies (NCS) revealed diffusely prolonged latencies, decreased conduction velocities, decreased distal amplitudes, and most notably, significant temporal dispersion and conduction block. This suggests an autoimmune demyelination neuropathy, though his clinical presentation was not strongly suggestive of one. Genetic testing confirmed a homozygous phosphoinositide phosphatase (FIG4) mutation.

Discussion: Charcot-Marie-tooth (CMT) disease is one of the most common inherited neurological diseases affecting approximately 1 in 2500 individuals. When significant evidence of demyelination is seen electrodiagnostically, both acquired and inherited causes should be considered. Generally, the appearance of significant temporal dispersion or conduction block indicates an acquired process as it requires partial involvement of a particular nerve that is not typical in inherited neuropathies. While useful, there are exceptions to this rule. One of these is CMT4J, affecting 0.24% of people with CMT, due to recessive mutations in the FIG4 gene.

Setting: Outpatient PM&R Clinic

Assessment/Results: Identification of the underlying inherited cause of his neuropathy allowed him to avoid further workup including a lumbar puncture and treatment trials including steroids or intravenous immunoglobulin (IVIg).

Conclusion: Abnormal temporal dispersion and conduction block generally indicate an acquired neuropathy, but electro-diagnosticians should consider inherited causes when the clinical picture is not suggestive of an autoimmune demyelination neuropathy.