Challenging diagnosis of resistance to thyroid hormone in a patient with COVID-19, pituitary microadenoma and unusual response to octreotide long-acting release test.

RTHβ is a rare genetic syndrome characterised by discrepant thyroid function tests and by a dissociation between the observed hormone levels and the expected patient signs and symptoms. Features of thyroid hormone deficiency in TR-ß dependent tissues (pituitary gland, hypothalamus, liver and neurosensitive epithelia), as well as thyroid hormone excess in TR-α-dependent tissues (heart, bone, skeletal muscle and brain), may coexist in the same individual. Clinical pictures can be different even when the same variant occurs, suggesting that other genetic and/or epigenetic factors may play a role in determining the patient's phenotype. Differentiating RTHβ from a TSH-secreting pituitary tumour is very difficult, especially when a concomitant pituitary adenoma is detected during diagnostic workup. The injection of long-acting somatostatin analogues can help differentiate the two conditions, but it is important to detect any interference in the dosage of thyroid hormones to avoid an incorrect diagnosis. Genetic testing is fundamental to prevent unnecessary and potentially harmful therapies. Medical treatment with triiodothyroacetic acid was demonstrated to be effective in reducing thyroid hormone excess and controlling symptoms.