Case Presentation: Case 1:A 55 year-old woman with a history of myasthenia gravis presented to with symptoms of double vision. She was also complaining of palpitations, weight loss, sweating, and insomnia. She was diagnosed with myasthenic flare, and she was treated with prednisone. The patient continued to have symptoms, so she was referred to an endocrinologist.
Exam showed symmetric enlargement of the thyroid gland, a fine tremor, mild exophthalmos and lid retraction.
Labs showed TSH 0.02, fT3 5.2, fT4 2.2, and TRAb was positive. The patient was started on Methimazole. On follow up, the patient was doing better and thyroid function test were back within normal ranges.
Case 2:
A 56-year-old woman with history of Graves hyperthyroidism with thyroid ablation presented with new symptoms of ptosis and diplopia. She also had dysphasia and multiple episodes of choking on food. She went and saw a neurologist who suspected myasthenia gravis. Lab works showed positive anti–acetylcholine receptor antibody, and a CT scan of the chest revealed a thymoma. After the patient underwent resection of the benign tumor, her myasthenic symptoms improved significantly and she did not require further treatment.
Discussion: Myasthenia gravis is an autoimmune neuromuscular disease where the immune system forms autoantibodies against post-synaptic acetylcholine receptors of the NMJ. Myasthenia gravis is characterized by skeletal muscle weakness that worsens with activity. Patients typically present with ocular and bulbar symptoms, proximal limb weakness, or some combination of these symptoms. Isolated neck, respiratory, or distal limb weaknesses are rarer manifestations. Additionally, 10-12 % of AChR antibody associated cases are found to have thymoma. Treatment includes acetylcholinesterase inhibitors, immunosuppression, IVIG, and thymectomy.
Graves’ disease is an autoimmune disorder in which antibodies target the thyrotropin receptor, resulting in overproduction of thyroid hormone and hyperplasia of the thyroid gland. Common manifestations include weight loss, heat intolerance, anxiety, tremor, diarrhea, and palpitations. Graves’ disease can be treated with antithyroid medications, radioiodine ablation, or surgery.
Though these two conditions are not often seen together, myasthenia gravis is present in 0.2% of patients with Graves’ disease, and conversely Graves’ disease is present in 5-10% of patients with myasthenia gravis. The presentation of these disorders is very similar. Muscle weakness, diplopia, and weight loss are common in both diseases. However, the presentation of myasthenia gravis generally lacks diarrhea, heat intolerance, and anxiety. If they are present it warrants a workup for hyperthyroidism in a patient with myasthenia gravis. Similarly dysarthria and respiratory muscle weakness, are symptoms that are not typically seen in hyperthyroidism. The presence of these symptoms warrant a workup for myasthenia gravis in a patients with Graves’ disease.
Conclusions: The co-presentation of myasthenia gravis and Graves’ disease can make the diagnosis of one or the other more difficult. These cases are presented in order to highlight that the presentation of one of these conditions in a patient can obscure the diagnosis of the other condition. If the diagnosis of these conditions is delayed, it can increase the morbidity to the patient.