TSH産生下垂体腺腫の2症例—内分泌学的検索および診断，治療方針に関する考察

Two Cases of TSH-secreting Pituitary Adenoma;Endocrinological, diagnostic and therapeutic approach to the disease

I．はじめに

　甲状腺機能亢進症の治療後，煙期間で発見され，かつT₃抑制試験に有意な反応を示したTSH産生下垂体腺腫を2例経験した．うち1例（症例1）は共著者が既に報告しているが^1），今回は術後の長期経過観察の結果を加え，改めて報告する．新たに経験した1例（症例2）では，甲状腺機能亢進状態にある初診時のCTでは認められなかった腺腫が，血中T₃，T₄濃度の正常化後にmacroadenomaとして発見され，初診時から術後に至るまで，詳細な内分泌学的検索を行い得た．

　TSH産生下垂体腺腫は現在まで約100例が報告されているが，T₃，抑制試験に有意に反応した例は極めて稀である．しかも甲状腺機能亢進症の治療後，短期間に発見された点とを考慮して，両症例は血中T₃・T₄濃度が腺腫の成長及びTSH分泌に影響を与えた事が示唆された，貴重な例であると思われる．TSH産生下垂体腺腫の診断・治療方針に関する考察を加えて報告する．

Abstract

Two cases of TSH-secreting pituitary adenoma were reported. Endocrinological and immunohistochemical features of these cases were described and problems in diagnosis and treatment of the rare disease are dis-cussed.

＜case 1＞ A 28 year-old woman suffered from hyper-thyroidism with a relatively high value of serum TSH (T₃ ; 350ng/dl, T₄ ; 10.0 μg/dl/, TSH ; 24.5 μU/ml) . She was treated with antithyroid drug and then under-went subtotal thyroidectomy.

Although the levels of serum T₃ and T₄ were lowered to within normal range, the level of serum TSH still remained high. One month later, she developed frontal headache, amenorrhea and bitemporal hemianopsia. A CT scan showed an en-hanced mass in the sellar and suprasellar region. Preop-erative endocrinological studies showed elevated values of TSH (47 μU/ml) and its α -subunit (9.0ng/ml). The levels of both T₃ (19Ong/dl) and T₄ (10.0 μg/dl) were near the upper normal limit. Serum TSH was suppres-sed by administration of exogenous T₃, but did not re-spond to exogenous TRH, l-Dopa nor bromocriptine. Under the diagnosis of TSH-secreting pituitary adeno-ma, the patient was operated on by craniotomy and re-ceived local radiation therapy (50Gy). In 1990, 12 years after the treatment, she is well and endocrinologically normal. Immunohistochemical study revealed that most tumor cells were positive for TSH.

＜case 2＞ A 28 year-old woman visited our hospital for examination of hyperthyroidism. Serum level of TSH was detectable (4.5 μU/ml) . A CT scan per-formed at that time disclosed no pituitary tumor. Thy-roid function was normalized by antithyroid drug, but the level of TSH was still high and progressively in-creased. One year later, a CT scan revealed an intrasel-lar tumor which was enhanced by contrast medium. Preoperative endocrinological studies showed a high value of both serum TSH (117.9 μU/ml) and its α-subunit (14.0ng/ml). Serum T₃ (105ng/dl) and T₄ (6.7 p g/dl) were within normal ranges. Serum TSH was increased by exogenous TRH. Both T₃ and somatosta-tin suppressed the elevated level of TSH, while gluco-corticoid, l-Dopa and bromocriptine did not affect serum TSH. Under the diagnosis of TSH-secreting pituitary adenoma, transsphenoidal selective ade-nomectomy was performed. On the day following the surgery, the values of serum TSH, T₃ and T₄ were re-markably lowered (TSH ; 1.9 μU/m/, T₃; 42ng/dl, T₄ ; 3.9 μg/ dl) Immunohistochemical study demon-strated that most tumor cells were positive for β-subunit of TSH.

These two presented cases of TSH-secreting pituit-ary adenomas are unique in that The secretion of TSH by these adenomas was suppressed by administration of exogenous T₃ and that relatively rapid growth of the adenomas might be induced by normalization of serum T₃ and T₄.

In order to disclose a microaclenoma, repeated ex-aminations of the sellar region by CT and/or MRI are essential in patients with hyperthyroidism combined with detectable levels of serum TSH, particularly in the follow-up period after treatment for hyperthyroidism.