Endocrine Abstracts

Introduction: TSHomas are rare TSH producing tumors, whereas chronic autoimmune thyroiditis is a frequent condition. Patients with TSHoma are characterized by increased circulating levels of peripheral thyroid hormones, but when a chronic autoimmune thyroiditis is associated, they may be normal or low, making the diagnosis challenging.

Case report: A 55 year-old woman, with previous medical history of obesity and impaired fasting glucose, was diagnosed of primary autoimmune subclinical hypothyroidism, with fT4 1.01 ng/dl (0.85–1.75), TSH 9.45 mUI/l (0.3–4.2) and positive anti-thyroid peroxidase antibodies. Levothyroxine treatment was started, but despite increasing doses with fT4 values over the normal range, normalization of TSH could not be achieved, therefore, she was sent to the Endocrinologist. She was under levothyroxine 150 μg/day, with fT4 1.87 ng/dl, fT3 4.2 pg/ml (2.0–4.4), TSH 54.56 mUI/l. She complained of asthenia and nervousness, with no other relevant symptoms. On suspicion of resistance to thyroid hormones and the asthenia, levothyroxine dose was increased to 175 μg/day, with subsequent blood test: fT4 1.93 ng/dl, fT3 4.3 pg/ml, TSH 40.90 mUI/l, free-α-subunit 370.8 mUI/mL (<1.3). Pituitary magnetic resonance imaging showed a big infiltrating tumor mass at the pituitary region. The rest of pituitary function was normal. She presented worsening visual impairment. Levothyroxine treatment was withdrawn, with fT4 0.92 ng/dl, fT3 3 pg/ml and TSH 413 mUI/l. Surgery was performed with a partial exeresis. Diagnosis of pituitary adenoma was confirmed, visual impairment improved, and TSH and free-α-subunit concentrations fell down to 49.2 mUI/l and 220.8 mUI/ml. Treatment with somatostatin analogues has been started.

Conclusions: TSHomas can be misdiagnosed if they coexist with chronic autoimmune thyroiditis. Normal peripheral thyroid hormones may cause us to not think of TSHoma as a cause, therefore, if increasing doses of thyroid hormone therapy do not achieve to normalize TSH, we always have to exclude a thyrotropinoma.