Anaplastic carcinoma accounts for <5% of thyroid cancer. The simultaneous occurrence of anaplastic carcinoma (ATC) and Gravess thyrotoxicosis is extremely uncommon with only six cases described in the literature.
A 73-year-old female presented with weight loss and atrial fibrillation. Investigations showed TSH-0.02 mU with T4-40 pmol/l and T3-16 pmol/l suggesting thyrotoxicosis.There was no thyromegaly or orbitopathy. TBII was elevated at 10.3 U/l suggesting Gravess disease. Carbimazole was commenced with good biochemical response followed by a 400 MBq dose of ablative I131. Post radioiodine hypothyroidism was managed with levothyroxine.
She presented four months later with severe respiratory distress. An anterior indurated neck mass was noted. CT showed a diffusely enlarged, heterogeneous thyroid gland with calcification causing laryngeal stenosis. Bronchoscopy revealed tracheal stenosis below the vocal cords due to external compression and tumour infiltration. FNAC was initially suspicious for papillary thyroid carcinoma but subsequent core biopsy immunohistochemistry was consistent with anaplastic thyroid carcinoma. Surgical debulking of the tumour was planned and an elective tracheostomy performed. However her condition deteriorated acutely due to a respiratory tract infection and concurrent acute coronary syndrome. Palliative care was instituted and the patient died a week later.
Discussion: Our case initially presented with Graves disease with no thyromegaly or palpable nodules and developed a massive tumour with compressive symptoms 8 months later. 12 to 26% of patients with GD are reported to have palpable thyroid nodule and 33.6% when detected ultrasonographically. Malignancy rate of nodule detected in association with Graves disease is 1017% and becomes higher if the nodule is palpable or scintigraphically cold. Most carcinomas associated with Graves appear to be papillary. There are case reports which show association with Gravess disease and ATC and it has been postulated that thyrotropin receptor antibodies promote transformation in well differentiated thyroid cancer. Further studies are warranted to clarify whether Graves disease or thyroid stimulatory receptor antibodies are independent risk factors for anaplastic transformation.