A Case Report of Immune Checkpoint Inhibitor-related Myofasciitis (P7-11.017)

Objective: To present a rare case of immune checkpoint inhibitor (ICI)-related myofasciitis and discuss its clinical management. Background: Neurological adverse events associated with ICIs are increasingly recognized, though myofasciitis remains rare. It manifests with symmetrical stiffness, swelling, and pain in the limbs, as well as restricted joint mobility. Management typically involves discontinuation of ICIs and initiating immunosuppressive therapy, often requiring a multidisciplinary approach. Design/Methods: We report a case of ICI-related myofasciitis and review the relevant literature. Results: A 64-year-old male with malignant melanoma received pembrolizumab therapy. In the tenth month of treatment, he began experiencing tightness and stiffness in the skin of his limbs, along with muscle atrophy and dependent edema in the lower extremities. He also reported fatigue, muscle pain, and restricted joint mobility during daily activities. The symptoms gradually worsened, and no rash or groove sign was observed. Laboratory tests revealed a mild increase in eosinophils, elevated erythrocyte sedimentation rate, and hypergammaglobulinemia. Creatine kinase levels were negative. Antinuclear antibody screening showed a positive titer of 1:160, along with anti-SSA/Ro-52 antibody positivity. MRI of the thigh muscles demonstrated diffuse thickening and enhancement of the fascia, with no myopathic changes noted on electromyography. Quadriceps muscle biopsy demonstrated fasciitis predominantly characterized by infiltration of CD4+ and CD68+ cells. There was also severe atrophy and degeneration of perifascial and perifascicular muscle fibers, accompanied by minimal necrosis and phagocytosis. Following consultation with oncologists, pembrolizumab was discontinued, and oral prednisone was initiated at a dosage of 1 mg/kg with gradual tapering. One month later, the patient reported slight symptom improvement, prompting the addition of methotrexate for immunosuppression. Conclusions: ICI-related myofasciitis is rare, with no established treatment guidelines. Management should consider experiences with other immune-related adverse events (irAEs) and primary eosinophilic fasciitis. Disclaimer: Abstracts were not reviewed by Neurology® and do not reflect the views of Neurology® editors or staff. Disclosure: Dr. Sun has nothing to disclose. Dr. Wu has nothing to disclose.