Disclosures: Kurt D. Wilhelm, MD: No financial relationships or conflicts of interest

Case Diagnosis: Tropomycin Receptor Kinase Inhibitor, Larotrectinib as a Contributing Factor to an Immune Mediated Polyneuropathy

Case Description or Program Description: Patient presented with subacute, progressive distal upper and lower extremity weakness, paresthesias and ataxia. Initial workup revealed albuminocytologic dissociation on LP, which was confounded by EMG showing chronic cervical polyradiculopathy without ongoing denervation. Consideration was given to an immune mediated polyneuropathy, possibly due to his chemotherapy drug larotrectinib. This agent was stopped and he was started on a five day course of IVIG with improvement in arm and leg strength, which plateaued after multiple subsequent IVIG treatments. After his admission to inpatient rehabilitation (IPR), the difficult decision was made to restart his chemotherapy agent. Ten days later, the patient’s manual muscle testing worsened, so his chemotherapy was stopped again and IVIG treatment was initiated early. After these interventions, manual muscle testing of his upper and lower extremities improved. This improvement again plateaued with subsequent pulse IVIG treatments.

Setting: Major Academic and Referral Center with Level 1 Adult Trauma

Assessment/Results: Repeat EMG on IPR revealed chronic cervical and lumbar polyradiculopathies as well as decreased amplitudes and prolonged F waves without temporal dispersion. Orthopedic surgery did not believe the patient’s moderate to severe cervical stenosis was significantly changed from prior on imaging. Anti-neoplastic workup was negative. Inflammatory markers were not significantly elevated.

Discussion (relevance): While this patient had many contributing factors to his neurologic weakness and ataxia, his neurologic examination showed improvement when the drug was stopped, both at initial admission and again while on inpatient rehabilitation. This case stresses the need for continued monitoring of the possible neurologic effects of monoclonal antibody treatments like this that have targets on the peripheral and central nervous system.

Conclusions: Patient’s symptoms improved with discontinuation of larotrectinib, which was deemed a potential contributing factor to an immune mediated axonal polyneuropathy.

Level of Evidence: Level V

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PM&R Meeting Abstracts - https://pmrjabstracts.org/abstract/tropomycin-receptor-kinase-inhibitor-larotrectinib-as-a-contributing-factor-to-an-immune-mediated-polyneuropathy-a-case-report/