Myasthenia, myocarditis, and myositis after checkpoint inhibitor therapy

In principle, side effects can affect all body systems and, under certain conditions, can be chronic or irreversible. Among the adverse effects of pembrolizumab, myocarditis and neuromuscular side effects are very rare, but are usually associated with a fulminant course and high mortality.

A 65-year-old man presented with a nodular melanoma of the left forearm. Histopathological examination after resection revealed the following parameters: absence of ulceration, Breslow depth 12 mm, moderate occurrence of tumor-infiltrating lymphocytes (TIL), tumor infiltration of the deep surgical margin, microsatellite status and indeterminate lymphatic vessel involvement. Histopathological stage was pT4a > 4.0 mm. Several NRAS mutations have been detected in the molecular profile. Ultrasound and PET scan of the left axilla revealed a 10-mm hypoechoic, vascularized lymph node that was metabolically active. Fine needle aspiration biopsy confirmed the clinical diagnosis of metastatic melanoma.
One month after the initial diagnosis, the resection margins were removed and an axillary lymphadenectomy was performed. Histological analysis of the skin was negative, but metastatic melanoma with extracapsular extension was found in one of the four lymph nodes examined (pN1b).