Disclosures: Tawnee L. Sparling, MD: No financial relationships or conflicts of interest

Case Diagnosis: Hereditary Neuropathy with Liability to Pressure Palsies (HNPP)

Case Description: A 25-year-old right-hand-dominant male presented to clinic with acute progressive, painless bilateral small finger numbness and weakness. Family history was negative for neurologic disorders.

Setting: Orthopedic Hand ClinicAssessment/

Results: Exam revealed signs of severe bilateral ulnar neuropathy: decreased sensation in the ulnar hand and weakness in bilateral first dorsal interossei, adductor digiti minimi and flexor digitorum profundus (4th/5th) muscles. Wartenberg and Froment signs were positive. Normal sensation and full strength in median and radial nerve distributions. Ultrasound revealed bilateral focal enlargement of the ulnar nerves at the elbow (CSA>10mm2). MRI was negative for focal compression. Electrodiagnostic studies showed severe focal demyelination and conduction block of bilateral ulnar nerves at the elbow and median nerves at the wrist. Patient was referred to a neuromuscular specialist. Genetic testing revealed heterozygous PMP22 deletion, consistent with HNPP. Patient was managed conservatively with activity modification and elbow pads with improvement.

Discussion: Severe bilateral sensorimotor ulnar neuropathy in a young adult is an unusual presentation more commonly seen in older individuals with comorbidities. It therefore necessitates electrodiagnostic work-up, which is less frequently ordered for younger individuals. Electrodiagnostic studies of bilateral median, ulnar and peroneal nerves and genetic testing are essential for diagnostic confirmation of HNPP, as presence of a hereditary neuropathy significantly changes management. Ultrasonography and MRI may show signs of focal nerve compression but are less useful to distinguish HNPP from typical compression. The benefit of ulnar nerve decompressive surgery in HNPP is not well established, as full spontaneous recovery has been reported in 50% of patients.

Conclusion: HNPP must be considered when young patients present with acute onset, severe painless mononeuropathy. As diagnostic imaging criteria for focal compressive neuropathies become more widely adopted, electrodiagnostic testing remains necessary to assess for HNPP. Surgical decompression of the nerve is often not recommended.

Level of Evidence: Level V

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PM&R Meeting Abstracts - https://pmrjabstracts.org/abstract/atypical-presentation-of-bilateral-ulnar-neuropathy-in-a-young-adult-a-case-report-of-hereditary-neuropathy-with-liability-to-pressure-palsies-hnpp/