副腎偶発腫瘍における褐色細胞腫の鑑別 : メトクロプラミド負荷試験と131I-MIBGシンチグラフィの有用性について

Abstract

1)副腎偶発腫瘍10例(褐色細胞腫6例, 内分泌非活性副腎皮質腺腫4例)に対し, i)24時間蓄尿による尿中内分泌学的検査, ii)メトクロプラミド負荷試験, iii)131I-MIBGシンチグラフィを施行し, 褐色細胞腫の鑑別における有用性を検討した. 2)全ての検査でspecificityは100%であったが, sensitivityは蓄尿による尿中内分泌学的検査が最も高かった. 3)副腎偶発腫瘍における褐色細胞腫の鑑別には, まず24時間蓄尿による尿中内分泌学的検査を行うべきである.しかし, 本検査に異常所見がない場合にも偽陰性例の可能性があるため, 画像診断等で褐色細胞腫が疑われる場合にはメトクロプラミド負荷試験や131I-MIBGシンチグラフィによる鑑別診断が必要となる

Pheochromocytoma accounts for approximately 25% of incidentally discovered adrenal masses. Certain diagnostic procedures (e.g., adrenal arteriography, needle biopsy of an adrenal mass), anesthesia and abdominal surgery may cause a sudden release of catecholamines from a pheochromocytoma and induce paroxysmal attacks of hypertension. In addition, pheochromocytoma is well known to cause unsuspected operating room deaths. Therefore, we must carefully separate this functioning neoplasm from other types of adrenal masses. In this study, we compared the results of noninvasive tests including (1) assay of urinary catecholamines and their metabolites, (2) a provocative pharmacologic test using metoclopramide (MCP test), and (3) 131I-metaiodobenzylguanidine (MIBG) scintigraphy to screen for pheochromocytoma in 10 consecutive patients with an incidentally discovered adrenal mass (6 pheochromocytomas and 4 non-functioning adrenocortical adenomas). We measured the 24-hour urinary excretion of catecholamines, metanephrines and vanillyl mandelic acid in all 10 patients; 5 were positive, 4 were negative and 1 was false-negative (sensitivity = 83%, specificity = 100%). The MCP test was performed in 7 patients; 3 were positive, 3 were negative and 1 was false-negative (sensitivity = 75%, specificity = 100%). MIBG scintigraphy was performed in 7 patients; 4 were positive, 1 was negative and 2 were false-negative (sensitivity = 67%, specificity = 100%). According to these results, all patients with an incidentally discovered adrenal mass should undergo a determination of the 24-hour urinary excretion of catecholamines and their metabolites, including metanephrines. If this urine assay is negative, other noninvasive tests including the MCP test and MIBG scintigraphy should be considered in selected patients with radiographic characteristics of pheochromocytoma.