Endocrine Abstracts

Background: Graves’ disease with ocular myasthenia are autoimmune disorders with their association being rare but well documented. There is overlap of ocular clinical features in both these conditions which can pose a significant clinical challenge. The diagnosis is necessary for both therapeutic and prognostic reasons.

Case presentation: A 35 year old lady presented with diplopia on downward gaze for 4 weeks. There is history of unintentional weight loss, variable mood, fatigue and palpitations. She is haemodynamically stable with mild tremor in both hands and no palpable goitre on neck examination. She has vertical diplopia with mild right eye proptosis, lid lag and bilateral ptosis. Systemic examination is unremarkable. Investigations revealed hyperthyroidism with TSH <0.01 mU/l (0.27–4.2); Free T4 63.2 pmol/l (12–22); Free T3 21.61 pmol/l (3.1–6.8); TPO antibodies 117 IU/ml (0–34); Thyrotropin receptor antibodies 11.9 U/l (1–1.8). She is treated with carbimazole for graves thyrotoxicosis. Due to ptosis MRI orbits was done which excluded thyroid eye disease. Tensilon test and single fibre electromyography were done which confirmed ocular myasthenia. CT thorax has excluded any thymoma. She is treated with pyridostigmine with improvement of diplopia.

Discussion: Autoimmune thyroid disease is present in 5–7.5% of myasthenia patients but myasthenia is present in only 0.2% of patients with thyrotoxicosis. The reason for this association is unknown though many postulated theories are present. They both have similar neuromuscular involvement which can be challenging for the physician. Ptosis is generally seen in myasthenia in contrast to thyroid ophthalmopathy. In our patient this is the giveaway sign which warranted us to investigate further to confirm the diagnosis of myasthenia in coexistent graves thyrotoxicosis.

Conclusion: The main objective of this case is to consider myasthenia in presence of ptosis or orbicularis oculi paresis in patients with thyroid eye disease.