BACKGROUND
Factitious thyrotoxicosis is not benign and can cause severe hypercalcaemia (1), thyroid storm (2,3), periodic paralysis (4) and myocardial ischaemia (5,6). Delays in diagnosis can lead to prolonged therapy with anti-thyroid medications.
METHODS
We report on a 37-year-old female social worker with longstanding hyperthyroidism, on a background of Hashimoto’s thyroiditis with positive TPO antibodies diagnosed at age 29.
RESULTS
At age 34, our patient presented with thyrotoxic symptoms including palpitations, fatigue, anxiety and alopecia, associated with TSH 0.01mU/L, fT4 58.4pmol/L, fT3 22.2pmol/L, undetectable TSH receptor antibody. Her regular levothyroxine dose of 50 micrograms daily was ceased and she was commenced on propranolol for symptomatic relief of suspected postpartum thyroiditis. Due to persistent symptoms and biochemical evidence of thyrotoxicosis, carbimazole was prescribed for presumed antibody-negative Graves’ disease. Thyroid scintigraphy was not undertaken due to breast-feeding, frequent non-attendance at outpatient clinics and her moving interstate. At age 36, she was changed to propylthiouracil 100mg TDS with ongoing beta blockade due to carbimazole-related nausea, rising fT4, from 30pmol/L to 58pmol/L in the context of consistent poor adherence. A pertechnetate thyroid scan at age 37 calculated thyroid uptake as 0.42% (normal 1-5%) with no appreciable tracer uptake. At this time, TSH was <0.01mU/L (reference 0.38-5.30), fT3 > 45pmol/L (reference 3.3-6.8), fT4 > 75pmol/L (reference 8-16.5), thyroglobulin concentration <0.10 ug/L (reference 1.6-50) and thyroglobulin antibody 48kunits/L (reference <4) associated with an elevated corrected calcium of 2.70 mmol/L (normal 2.10-2.60) and ongoing severe symptoms of hyperthyroidism preventing employment including depression. Whole body I-131 uptake scan revealed absent tracer in the thyroid bed without ectopic I-131 avid thyroid tissue, excluding struma ovarii and confirming the most likely diagnosis of factitious thyrotoxicosis. She denied taking levothyroxine or iodine-containing supplements and had no known iodinated contrast exposure.
CONCLUSION
Factitious thyrotoxicosis is a crucial differential in refractory hyperthyroidism.