Disclosures: Malav P. Shah, MD: No financial relationships or conflicts of interest

Case Diagnosis: Posterior Interosseous Neuropathy due to Intramuscular Lipoma

Case Description: : The patient presented with 8 months of left-hand numbness and tingling. Her symptoms progressed to decreased dexterity and weakness. Examination and cervical spine radiographs were within normal limits. Magnetic Resonance Imaging (MRI) revealed multilevel disc protrusions and uncovertebral hypertrophy causing moderate foraminal with no central canal stenosis. One month later, she reported worsening of her symptoms, including inability to extend her fingers. Exam showed 0/5 strength in finger extensors and finger abductors and radially deviated wrist extension. Electrodiagnostic testing showed Posterior Interosseous Nerve (PIN) neuropathy with axon loss secondary to radial nerve compression at the elbow. She then felt a mass in the proximal forearm and plain radiographs showed a soft tissue radiolucent area around the radial head. MRI revealed a 3.3cm mass that wrapped around the radial neck and extended between the radius and ulna.

Setting: Outpatient Spine Clinic in an Orthopedic PracticeAssessment/

Results: Surgical removal of the mass with associated neurolysis of the posterior interosseous and superficial sensory radial nerves was performed 6 weeks after diagnosis without any complications. Pathology confirmed benign lipoma. Post-operatively, she continued to have digit extension weakness. After 3 months she reported 70% recovery of finger extension strength and was able to perform most activities of daily living.

Discussion: Few cases of PIN neuropathy due to compressive lipoma have been described in the literature. Electrodiagnostic studies and MRI are useful in identification and management of the pathology.

Conclusion: A high index of suspicion is needed for early diagnosis of posterior interosseous neuropathy. Further workup if no obvious cause is immediately identified, or if cervical spine imaging is normal, should include electrodiagnostic studies and evaluation for a compressive mass. Early diagnosis and treatment is likely to result in better of functional recovery, as seen in our patient.

Level of Evidence: Level V

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PM&R Meeting Abstracts - https://pmrjabstracts.org/abstract/posterior-interosseous-neuropathy-due-to-intramuscular-lipoma-a-case-report/