Ectopic thyroid stimulating hormone (TSH)oma located outside the sella turcica is exceedingly rare and can be associated with significant diagnostic delay. Clinical presentation depends on anatomical location and size of the ectopic tumour and degree of thyrotoxicosis.
A 71-year-old female presented with goitre and thyrotoxicosis. Initial investigations revealed elevated free thyroxine (fT4) of 21.6 pmol/L and tri-iodothyronine (fT3) of 5.8 pmol/L with inappropriately high-normal TSH OF 3.8 mIU/L. Remainder of the pituitary panel was unremarkable. Assay interference was deemed unlikely, pituitary magnetic resonance imaging (MRI) scan was reported as ‘normal’ and germline sequencing was negative for thyroid hormone receptor ß pathogenic variants. One-year later, total thyroidectomy for enlarging symptomatic goitre and suspicious nodule revealed multifocal microscopic papillary thyroid carcinoma. Post-thyroidectomy, TSH was difficult to suppress despite thyroxine replacement (2mcg/kg/day).
Six-years later, she presented to an ear, nose and throat surgeon with nasal congestion and a sphenoid bone mass was discovered on naso-endoscopy. MRI scan of the head revealed a 3cmx2.3cm mass within the sphenoid bone. Ectopic TSHoma was confirmed on surgical resection with strong diffuse staining for chromogranin A, synaptophysin, Pit1 and TSH. Retrospective review of the initial pituitary MRI scan revealed a 2.3cmx2.2cm sphenoid mass which had initially been missed.
This is the first reported case of an ectopic TSHoma located in the sphenoid bone. Review of all 14 reported ectopic TSHoma cases (1-13) revealed the most common location as nasopharynx (9/14) and most common presentation as inappropriate TSH secretion and nasal congestion with median 2.5-year diagnostic delay. Surgical resection is generally complete without risk for post-operative hypopituitarism.
Ectopic TSHoma, which can be clinically and biochemically indistinguishable from pituitary TSHoma, should be considered in patients with inappropriate TSH secretion when more common differentials are excluded e.g. thyroid hormone resistance or pituitary TSHoma.