Title: A Rare Case of Concurrent Grave's Disease and Myasthenia Gravis Causing Respiratory Fatigue
Case Report Body:
Introduction: Autoimmune diseases are an under appreciated etiology of respiratory muscle weakness. Two prominent autoimmune diseases which have been associated with respiratory failure include myasthenia gravis (MG) and Grave’s disease. Very rarely, these two entities can present in the same patient, with myasthenia gravis reported in up to 0.35% of patients with Grave’s disease. Here we present the rare case of a patient with Grave’s disease who was incorrectly diagnosed with thyrotoxic periodic paralysis (TPP) and later found to have concurrent myasthenia gravis.
Description: A 23 year old female with past medical history of Grave’s disease presented with diffuse weakness, diplopia, and dysphagia in the setting of medication non adherence. Initial labs were significant for an undetectable TSH, free T4 of 3.4, and potassium of 3.6. A presumptive diagnosis of TPP was made and the patient was started on antithyroid medication, along with potassium replacement. Despite having improvement of her potassium and thyroid labs, the patient continued to have significant weakness. Due to concern for impending respiratory failure, the patient was transferred to ICU for close monitoring of her PFTs. Her acetylcholine receptor binding antibody returned positive and she was diagnosed with concurrent MG. The patient was then started on pyridostigmine and IVIG. Afterward, the patient’s weakness improved and she was eventually able to tolerate a regular diet. A chest CT was performed which showed a 10x4x2cm mediastinal mass, likely representing a thymoma. She was discharged on stable doses of medications for her diseases, with plans for close endocrinology, neurology, and CT surgery follow up.
Discussion: About 10-15% of patients with myasthenia gravis (most commonly adolescent females) suffer from concurrent autoimmune thyroid disease. Both MG and Grave’s are associated with T cell activation leading to autoantibody production. Untreated Grave’s disease can frequently precipitate a myasthenic attack, as was seen in our patient. Neurological manifestations of both diseases can overlap, with patients sharing features such as proximal muscle weakness and bulbar symptoms. Care must be taken when treating a patient with both diseases, as drugs used to treat one disorder (such as beta blockers or steroids) can frequently exacerbate the other.