Disclosures: Robert Lombard, MD: No financial relationships or conflicts of interest

Case Diagnosis: Charcot-Marie-Tooth 4J

Case Description: A 17 year old female with a history of CMT 4J secondary to homozygous FIG4 (exon 2, c. 112T >C (p.Ile41Thr)) mutation presented with 1 month of acutely worsening lower extremity weakness and new onset hand weakness after discontinuing immunotherapy. Neuromuscular ultrasound (NMUS) was performed in conjunction with an electrodiagnostic (EDX) study which demonstrated patchy asymmetric segmental enlargement in the tibial nerve at the popliteal fossa and ankle, the median nerve at the wrist and antecubital fossa, the ulnar nerve at the forearm, the brachial plexus trunk, and C5 nerve root. EDX findings also demonstrated a segmental picture with significant progression of the disease process as manifested by decreased motor response with slowed conduction velocities, conduction block, and decreased amplitudes as compared to one year prior.

Setting: Vidant Medical Center, Pediatric Rehabilitation UnitAssessment/

Results: NMUS and EDX demonstrate segmental demyelination with significant progression in comparison to EDX studies performed one year prior.

Discussion: FIG4 mutations are a rare cause of Charcot-Marie-Tooth disease which causes a congenital primarily demyelinating polyneuropathy. The estimated prevalence is 1/2500, with 90% of cases demonstrating autosomal dominate inheritance. Unlike more common variants of CMT, CMT 4J resembles an acquired segmental demyelinating process as opposed to the typical presentation of a uniform demyelinating process. Diagnosis is made through history, physical exam, and nerve conduction studies. Ultimately genetic testing is required for diagnosis. NMUS has potential as a diagnostic modality in this syndrome because it may show a different pattern of nerve enlargement relative to other CMT phenotypes. Leading with NMUS may be a way to guide both the EDX study and genetic testing in this condition.

Conclusion: CMT4J is a rare disorder of the peripheral nervous system. NMUS should be considered as a first step in evaluation of rare genetic disorders given that it is well tolerate and inexpensive.

Level of Evidence: Level V

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PM&R Meeting Abstracts - https://pmrjabstracts.org/abstract/neuromuscular-ultrasound-with-emg-ncs-to-evaluate-rapidly-progressing-symptoms-in-a-17-year-old-female-with-cmt-4j-due-to-homozygous-fig4-mutation/