dromlakhani Administer thyroid block for 123I-MIBG scintigraphy in pheochromocytoma and paraganglioma
STEP 1 — Gather Information
Confirm that 123I-MIBG scintigraphy is ordered for PPGL evaluation; assess for known iodine allergy, thyroid disease, or other contraindications to iodine supplementation. If the study is ordered and no absolute contraindication is identified, proceed to evaluate need for thyroid blockade.
STEP 2 — Rule In / Rule Out
Determine if the patient has a contraindication to iodine (e.g., severe iodine allergy, active thyroid storm, or known iodine-induced thyrotoxicosis). If a contraindication is present, rule out thyroid block; otherwise, rule in thyroid block administration.
STEP 3 — Classify or Stratify
Select the thyroid blocking agent: potassium iodide 50–150 mg orally once daily or Lugol's solution 5–10 drops orally once daily, based on availability and patient preference.
STEP 4 — Decide
Initiate the chosen thyroid block three days before the scheduled 123I-MIBG scintigraphy and continue daily dosing until and including the day of the scan.
Clinical Guardrails / Mimics / Pitfalls
Do not start thyroid blockade less than three days prior to scintigraphy, as inadequate blockade may fail to reduce thyroid uptake; do not discontinue before the scan day, which could increase thyroid radiation exposure; avoid iodine blockade in patients with documented severe iodine allergy; monitor for thyroid dysfunction in patients with underlying thyroid disease, though blockade is generally short-term.
Concrete Clinical Example
A 48-year-old patient with biochemical evidence of PPGL undergoes 123I-MIBG scintigraphy; the clinician orders potassium iodide 100 mg daily starting three days prior to the scan and continuing through the scan day to minimize thyroid radiation dose.
Source: Clinical Practice Guideline for the Diagnosis and Management of Pheochromocytoma and Paraganglioma, Japan Endocrine Society, 2025, doi:10.1507/endocrj.EJ25-0165