TSH-Secreting Adenoma


Question

I recently saw a 16-year-old lady referred for abnormal thyroid function tests. A year ago, she noticed increasing hair loss off the top of her head. She was also complaining of fatigue and cold intolerance. No weight loss, no loose stools. She noticed an increased frequency of parietal headaches, 2-3 times weekly. She has regular menses with no breast discharge. She is on Depo-Provera every 90 days. She has had 3 "blackout spells", periods of sudden LOC, lasting < 1 minute, with slight confusion on waking. Neurologic workup and EEG negative. Brain MRI negative. Initial TSH (12/16/2009) = 1.55 (range = 0.35-5.50).

Went back to her PCP and repeat labs in 11/27 showed TSH = 1.750, Free T4 = 1.990 (range = 0.930-1.700). I saw her 2 days after these labs were drawn. I ordered labs on 11/29 with the following results:

Free T3 = 480 pg/dL (range = 230-420)

Thyroid binding Globulin = 24.1 ug/ml (range = 10.0-23.8)

T3 uptake = 35% (range = 22-35)

Total T4 = 11.8 mcg/dL (range = 4.5 - 12.5)

Free T4 by direct dialysis = 3.0 ng/dl (range = 1.0-2.4)

Thyroid-Stimulating Immunoglobulin = <89% (range <140%)

Thyroid US = Right lobe 5.5 cm, left lobe 5.2 cm. Small 1.1 cm nodule on the right. 6 mm hypoechoic nodule in the isthmus.

Pituitary MRI = Within the sella and extending superiorly toward the suprasellae cistern with an upwardly convex margin is a 9 x 10 x 9 mm homogeneously enhancing mass in the anterior aspect of the sella, essentially replacing the normal anterior lobe of the pituitary. On the sagittal images, there is a thin crescentic focus of decreased enhancement which likely separates this lesion from normal pituitary gland.

The high free T4 and free T3, with an inappropriately normal TSH, and a pituitary macroadenoma would suggest TSH-secreting tumor. I will be doing the pituitary hormonal workup. I will also do an FNA of the thyroid nodule. Given the relatively small size of the tumor, would this still be amenable to trans-sphenoidal resection?

Is differentiation from Resistance to Thyroid Hormone required in this case? Would you recommend a T3 suppression test? Are there any other labs you would recommend to confirm the diagnosis? Sincerely, Patrick Litonjua, MD

Response

There are no doubts that the patient has a TSHoma. To confirm the diagnosis we usually ask for the measurement of FT4 and TSH in the closer relatives and we perform a TRH test (no TSH response definitely confirm the presence of TSHoma). Unfortunately TRH is no longer available in the States. I suggest, therefore, to send the young lady to the neurosurgeon. Alternatively, you can treat her with long acting somatostatin analogs that are effective in blocking TSH secretion in more than 90% of cases and may cause tumor shrinkage in more than 50% of cases. Let me know of your decision. Paolo Beck-Peccoz, MD