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Indian Journal of Medical Sciences, Vol. 61, No. 6, June, 2007, pp. 357-359 Letter To Editor Myasthenia gravis and autonomously functioning thyroid nodule - a rare association Pradeep PV, Agarwal Amit, Jain Manoj, Gupta SushilK Department of Endocrine Surgery, Sanjay Gandhi Postgraduate Instutute of Medical Sciences, Lucknow Code Number: ms07058 Sir, A 45-year-old diabetic lady presented to our institute in June 2004 with complaints of thyroid swelling of 14 years′ duration. The patient had ptosis and generalized episodic weakness of muscles, which aggravated towards the evening. She was diagnosed to have hyperthyroidism, as evidenced by her thyroid function tests. Radionuclide thyroid scan revealed an autonomously functioning thyroid nodule (AFTN) [Figure - 1]A. Antimicrosomal antibody was weakly positive (1/400). Myasthenia gravis was diagnosed by the neostigmine stimulation test. We do not routinely employ fine needle aspiration cytology for hyperthyroid patients. CT neck revealed a solitary nodule in right lobe of thyroid [Figure - 1]B. CT scan thorax did not reveal any mass lesion [Figure - 2]A. The patient was started on antithyroid drug [Neomercazole (NMZ) 15 mg] and anticholine-esterases (Pyridostigmine) 180 mg/day. Radioiodine therapy (8 mCi) was done for the AFTN, resulting in hypothyroidism in 2 months. She developed myasthenic crisis in August 2004 requiring ventilation. Subsequently, neostigmine 45 mg was added and a trans-sternal thymectomy performed (January 2005). Thymus weighed 20 gm [Figure - 2]B, and histopathology revealed lympho-follicular hyperplasia. At 23 months of follow-up, the patient is doing well on pyridostigmine 90 mg/day and TSH level of 4.4 mIU/l. Even though myasthenia gravis (MG) is associated with many autoimmune diseases, the association of MG with autonomous functioning thyroid nodule (AFTN) is very rare. We could come across only one such report so far in the English literature, which was published in 1966 by Recordier et al. [1] We report this case for its rarity. As many as 70-80% of myasthenic patients have thymic hyperplasia and 15% have thymoma. Epidemiological studies showed that autoimmune thyroid disease occurs in approximately 5-10% of MG patients, [2] but the association with AFTN has rarely been reported. AFTN is known to be caused by two somatic mutations which involve the Gs alpha protein and the TSH receptor; however, in geographical areas of moderate iodine deficiency, the mutation in the latter gene is the major cause in more than 80% of the cases. [3] Whether such mutations can be triggered by autoimmune diseases needs to be addressed. Whether the association between MG and AFTN is an etiologically related one or a chance correlation is not clear. AFTN has to be tackled first due to its various grave metabolic implications with either radioactive iodine or hemithyroidectomy. These two modalities have not been compared in any randomized clinical trials. [4] In our patient, thyrotoxicosis was controlled with NMZ and subsequently ablated with radioiodine. The patient developed myasthenic crisis in spite of anticholine-esterases and hence she underwent thymectomy later. Patients who have large-sized AFTN will have to undergo hemithyroidectomy after the control of toxicity. No definite guidelines have been laid down to manage such association. Presence of hyperthyroidism or hypothyroidism is known to aggravate myasthenia gravis. [5] It is therefore possible that the unpredictable hypothyroidism, which can happen during or after radioiodine therapy, can aggravate the MG. Hemithyroidectomy for AFTN and thymectomy for myasthenia can be combined. References
Copyright 2007 - Indian Journal of Medical Sciences The following images related to this document are available:Photo images[ms07058f1.jpg] [ms07058f2.jpg] |
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