Case Author(s): Feiyu Xue, M.D., Ph.D. and Tom R. Miller, M.D., Ph.D. , 6/27/04 . Rating: #D2, #Q3
Diagnosis: Drug interference with MIBG uptake
Brief history:
47-year-old female with significantly increased metanephrine levels and hypertension.
Images:
MIBG Scintigraphy
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Full history/Diagnosis is available below
Diagnosis: Drug interference with MIBG uptake
Full history:
47-year-old female with significantly increased metanephrine levels and hypertension, suspected to have pheochromocytoma. An outside CT examination of the abdomen and pelvis demonstrate a 3 cm left adrenal mass and a 4-5 cm right retroperitoneal mass adjacent to the medial aspect of the right kidney. I-123 MIBG imaging is requested to evaluate for pheochromocytoma.
Radiopharmaceutical:
9.9 mCi I-123 MIBG
Findings:
There is an abnormal degree of MIBG uptake in the muscles throughout the body, and the expected mild uptake of MIBG in the myocardium is not seen.
Discussion:
Meta-iodobenzylguanidine (MIBG) is an analog of norepinephrine and is taken up selectively by the adrenal medulla, the sympathetic autonomic nervous system, and tumors derived from these tissues. Uptake occurs chiefly via the energy-dependent type I amine uptake mechanism. Many drugs interfere with uptake of MIBG, particularly tricyclic antidepressants, sympathomimetics (e.g., pseudoephedrine), and certain antihypertensives (labetalol, reserpine, and calcium channel blockers). This patient was prescribed Labetalol for hypertension. Labetalol is an alpha-1 and non-selective beta blocker, which is known to compete with MIBG binding and reduce sensitivity of MIBG Scintigraphy. An important indicator of an acceptable MIBG uptake is the presence of cardiac activity.
Reference:
Bombardieri E, Maccauro M, De Deckere E, Savelli G, Chiti A. Nuclear medicine imaging of neuroendocrine tumours. Ann Oncol. 2001;12 Suppl 2:S51-61.
Followup:
Major teaching point(s):
Because of interference of Labetalol with MIBG binding, this study was non-diagnostic. Because I-123 MIBG is very expensive particular effort should be made to insure that the referring physician and patient understand the importance of avoiding potential drug interaction and keeping the imaging appointment.
ACR Codes and Keywords:
References and General Discussion of MIBG Scintigraphy (Anatomic field:Gasterointestinal System, Category:Other(Artifact))
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Case number: mb006
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