Objective:

To illustrate a case of co-occurrent amyotrophic lateral sclerosis (ALS) and myasthenia gravis (MG) and the importance of clinical judgment in interpreting serologic/electrodiagnostic testing.

Background:

ALS is a motor neuron disorder presenting with progressive weakness with both lower and upper motor neuron findings. MG is an autoimmune neuromuscular junction (NMJ) disorder, which presents with fatigable weakness among other features. Approximately 0.75% of ALS patients are affected by MG, indicating overlap of rare disorders. Antibody testing against acetylcholine receptors (AChR), fatigable weakness, and significant (>10%) decrement on repetitive nerve stimulation (RNS) support diagnosis of MG. Significant decrement on RNS may be seen in ALS, and up to 5% of ALS patients harbor AChR antibodies. Clinical correlation is key in appropriate diagnosis and subsequent treatment. 

Design/Methods:

Case report and literature review.

Results:

An 80 year old man with 3 years of fatigable dysarthria and dysphagia was found to be AChR binding antibody positive. Pyridostigmine provided no benefit. Symptoms progression required hospitalization and treatment with 5 days of IVIG (2g/kg), and ultimate diagnosis of AChR positive MG. Over several months, he developed progressive head drop, sialorrhea, hyperreflexia, and muscle atrophy which did not respond to repeat IVIG. EMG/RNS showed diffuse, acute and chronic neurogenic changes, and  >10% decrement in 2 muscles, meeting criteria for definite ALS and NMJ dysfunction. He initiated riluzole, though transitioned to hospice and died shortly after dual diagnosis.  

Conclusions:

ALS and MG have different pathophysiology, prognosis, and treatment, despite overlap in serologic and electrodiagnostic testing. Co-occurrence is rare, though should be considered a possibility when clinical features of both are present.  Our patient had MG, responsive to immunotherapy, which progressed to a phenotype more consistent with ALS.  This case highlights the importance of clinical correlation to avoid misdiagnosis and to recognize rare combination of disorders, to tailor appropriate treatment regimens.