Dialysis
patients have ups and downs of blood pressure and a diagnosis of
pheochromocytoma(PH) is always challenging. Screening for PH is always a tough
challenge in non CKD/ESRD patients. It is even more challenging in ESRD
patients. Many
medications can interfere with measurements of catecholamine levels. Tricyclic
antidepressants interfere most frequently with the interpretation of plasma
fractionated metanephrines and 24-hour urinary catecholamines and metabolites. Most of these should be tapered and
discontinued at least two weeks before any hormonal assessments.
In
general, the approach to diagnosis is initial biochemical testing based upon
the index of suspicion that the patient has a PH. If there is a low index of suspicion,
a 24-hour urinary fractionated catecholamines and metanephrines; if there is a
high index of suspicion, a plasma metanephrine level should be done. The
endocrine society clinical practice guideline suggests initial biochemical
testing using 24-hour urinary fractionated metanephrines or plasma fractionated
metanephrines (drawn supine with an indwelling cannula for 30 minutes).
However, many times the measurement of plasma fractionated metanephrines is not
done under these conditions, and the test is associated with a high
false-positive rate.
Biochemical tests in renal disease might not be valid. In
patients without PH who are receiving dialysis, plasma norepinephrine and
dopamine concentrations are increased threefold and twofold above the upper limit of normal, respectively. When patients with CKD
have plasma norepinephrine concentrations more than threefold above the upper
normal limit or epinephrine concentrations greater than the upper normal limit,
PH should be suspected. It is hard to distinguish PH just with plasma
metanephrines in ESRD and CKD patients. Studies done have shown mixed results. Most ESRD patients are anuric and hence
urinary studies are not available. A
new biomarker has been recently discovered in the world of PH- Plasma
methoxytyramine. This is still not used in routine practice and data
on ESRD-CKD is not available to my knowledge.
What about the imaging
studies?
CT dedicated to the
adrenals or MRI of the abdomen and pelvis is usually performed first. Either
test is a reasonable first test as both detect almost all sporadic symptomatic
tumors because most are 3 cm or larger in diameter. If abdominal and pelvic CT
or MRI is negative in the presence of clinical and biochemical evidence of PH, think
of a perhaps a different diagnosis. If it is still considered likely, then
iodine-123 (123-I) iobenguane (also known as metaiodobenzylguanidine [MIBG])
scintigraphy may be done. MIBG is a compound resembling norepinephrine that is
taken up by adrenergic tissue. Normal adrenal glands take up MIBG, and the
uptake may be asymmetric. One prior paper showed perhaps a false
positive scan in ESRD. No newer studies have shown this. No specific studies have looked at MIBG scans in ESRD
patients except one case series from Japan.
Finally, FDG-PET scan is
more sensitive than 123-I MIBG and CT/MRI for detection
of metastatic disease. A scan called 68-Ga DOTATATE PET — Gallium 68 (68-Ga)
1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-octreotate
(DOTATATE)-positron emission tomography (68-Ga DOTATATE PET) is proving to be more
sensitive in some patients than 123-I MIBG, CT/MRI,
or FDG-PET for detection of metastatic disease.
So what does one do finally
for a CKD-ESRD patient?
If the plasma metanephrines
are threefold the upper limit of normal and there is an abnormal CT scan or MRI
localizing a lesion in one of the adrenals( depending on contrast load), a MIBG
scan is reasonable. If that is positive, there is a good chance that it is a
PH. Surgery decision should not be based solely on MIBG scan alone. A PET scan
or a TATE scan might be required to confirm the diagnosis in the grey zone of
CKD-ESRD and diagnosis of a PH.
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