To report a case on immune check- point inhibitor (ICI) immune-mediated neuromuscular overlap syndrome (myositis, myasthenia gravis, myocarditis) with findings of bilateral pterigoid myositis on MRI brain.

Since the introduction of ICI several years ago, neurologists encountered immune-related adverse events (irAEs) affecting both central and peripheral nervous system, with prior case series describing neuromuscular overlap syndrome

An 81-year-old man who completed two courses of Pembrolizumab subsequently subacutely developed ptosis, ophthalmoparesis, diplopia, motor weakness and eventually dyspnea and dysphagia. MRI brain revealed nonspecific white matter changes and symmetric edema and enhancement of bilateral pterygoid muscles. Further laboratory tests revealed elevated transaminases, CK at 3860 U/l, troponin elevation to 2661pg/ml and absent MG  and myositis antibodies.  ECG revealed new right bundle branch block.  He was empirically started on pyridostigmine and methylprednisolone. Plasma exchange was then attempted but terminated due to gastric bleeding. IV immunoglobulin (IVIG) was then added to IV methylprednisolone.  However, over several weeks he developed worsening dyspnea and bulbar symptoms requiring intubation and gastrostomy placement.  Despite improvement in ophthalmoparesis he was notable to be liberated from ventilatory support. Repeat MRI brain was obtained and images from initial study were compared. The bilateral pterygoid muscles edema and enhancement suggestive of myositis on initial MRI, has been resolved on repeat study.

Our patient was diagnosed with immune-mediated neuromuscular overlap syndrome also termed “triple M syndrome”, in association with ICIs.  Our patient demonstrated typical ocular-bulbar phenotype and interesting findings of bilateral pterygoid myositis that was reversed with treatment.  Unfortunately, despite radiological improvement, the clinical improvements were not significant.