Immune checkpoint inhibitors (ICIs) like Pembrolizumab (KEYTRUDA), an anti-PD-1 antibody, have dramatically changed treatment of advanced and metastatic malignancies. Myasthenia gravis (MG) and myositis have been reported as adverse effects of ICIs. We report a case of pembrolizumab-induced myositis in a patient with urothelial carcinoma.

CASE:

A 75 year old female with metastatic urinary bladder cancer presented with rapidly progressive ptosis, double vision, difficulty in swallowing and proximal muscle weakness for 10 days. She received two doses of Pembrolizumab with the last dose two weeks prior to presentation. She had bilateral ptosis, ophthalmoparesis, weak neck flexion, MRC grade four proximal muscle weakness of all limbs, +1 reflexes and flexor planters on examination. There was minimal improvement of ptosis with ice pack test. Labs showed creatinine kinase (CK) of 7500 IU/L and negative acetyl choline receptor (AChR) antibodies. She required intensive care monitoring and BiPAP for respiratory failure. She was treated with pyridostigmine, steroids and plasma exchange for six days with no significant improvement. Comfort care measures were initiated and patient passed away one week following presentation.

Our patient suffered from pembrolizumab-induced myositis. AChR antibodies were negative and she didn’t respond to pyridostigmine or immunotherapy. She had minimal improvement with ice pack test. Pembrolizumab-induced myositis is associated with Myasthenia gravis in 45% of cases and with myocarditis in 29%. Ten cases of ICIs-related myositis were reported by Touat et al. They presented with myalgia (8 patients) and limb-girdle (7), axial (7), and oculomotor (7) weakness. They all had negative AChR antibodies, high CK levels and electrodiagnostic studies showing myopathic changes without decrement.

Myositis and MG are important complications of treatment with Immune checkpoint inhibitors. They should be considered in patients presenting with neurological symptoms in the setting of ICIs use.