මේක රූල් අවුට් කර ගන්න තමයි ඕනේ.
SNRI බොන ගමන් metanephrine test එක කරන්න බැහැ. SNRI cold turkey නවත්තන්නත් බැහැ.. ඒකයි ප්රස්නේ මේකට මොකක්ද කරන්නේ කියන එක
Key challenge:
SNRIs (e.g., venlafaxine, duloxetine, desvenlafaxine, milnacipran, levomilnacipran) increase synaptic norepinephrine and can raise circulating catecholamines and
metanephrines, the very analytes used to screen for pheochromocytoma. This produces frequent
false-positive biochemical tests. The goal is to obtain at least one reliable set of results uncontaminated by the drug.
- Temporarily withdraw or switch the SNRI
• If the psychiatric risk is low to moderate,
taper off the SNRI for ≥2 weeks (≈5 half-lives) before drawing blood or collecting 24-h urine.
– Venlafaxine & desvenlafaxine: 5–7 days minimum; 14 days preferred.
– Duloxetine: 7–10 days minimum; 14 days preferred.
• Manage withdrawal with a short taper (reduce dose every 2–3 days) and start an
SSRI (sertraline, escitalopram, fluoxetine) or buspirone if an antidepressant is still needed; these do
not interfere with catecholamine testing.
• If stopping the SNRI is unsafe (high suicide risk, refractory depression):
- Obtain psychiatric clearance for a closely supervised taper that lasts as short as clinically feasible, or
- Proceed to alternate biochemical or functional tests (see below).
- Choose the least drug-sensitive biochemical test
• First-line after drug washout:
Plasma free metanephrines measured after the patient rests supine for 20–30 min in a quiet room. (Superior sensitivity; modest increase from SNRIs resolves after washout.)
• If the SNRI cannot be stopped:
–
24-h urinary fractionated metanephrines tend to be
less affected than plasma catecholamines but still show some false positives.
–
Chromogranin A is unaffected by SNRIs but has lower specificity; use only as adjunct.
–
Urinary 3-methoxytyramine (3-MT) is not influenced by SNRIs and can help rule out head-and-neck paragangliomas, although data are limited.
- Consider a functional suppression test (second line)
•
Clonidine suppression test (for borderline‐elevated plasma catecholamines):
– Give oral clonidine 0.3 mg after baseline catecholamine draw.
– Measure plasma catecholamines again at 3 h.
– In true pheochromocytoma,
norepinephrine stays elevated; in drug-induced elevation it suppresses by ≥40 % or to <500 pg/mL.
– Ensure normal blood pressure and cardiac status before using clonidine.
- Imaging only after unambiguous biochemical confirmation
• CT/MRI adrenal or extra-adrenal, and ¹²³I-MIBG or ⁶⁸Ga-DOTATATE PET, should be performed
only when biochemical evidence persists after drug washout or alternate testing confirms excess catecholamine production.
- Practical workflow summary
- Psychiatric review → plan SNRI taper (aim ≥2 weeks off).
- During washout: monitor for discontinuation syndrome; cover with SSRI if needed.
- After washout: draw plasma free metanephrines with proper supine rest.
- If still positive or SNRI cannot be stopped:
• Repeat test with urinary metanephrines ± 3-MT
• Add clonidine suppression test.
- Proceed to imaging only if biochemical tests remain positive.
Take-home point:
Because SNRIs reliably elevate catecholamine measurements,
the simplest and most reliable way to rule out pheochromocytoma is to stop the SNRI long enough for it to clear, then repeat high-sensitivity plasma free metanephrines under standardized conditions. When withdrawal is impossible, combine the least drug-sensitive analytes with a functional suppression test to reach a confident conclusion.