From the Guidelines
Pheochromocytoma can indeed be missed by regular tests due to its intermittent hormone secretion and ability to mimic other conditions. According to the most recent guidelines, phaeochromocytomas are rare adrenal tumors that secrete catecholamines and are present in less than 0.2% of patients with hypertension 1. The diagnosis of pheochromocytoma should be entertained in a hypertensive patient with a combination of headaches, palpitations, and sweating, typically occurring in an episodic fashion, with a diagnostic specificity of 90% 1.
Key Points to Consider
- The best screening test for pheochromocytoma is plasma free metanephrines (normetanephrine and metanephrine), which carries a 99% sensitivity and an 89% specificity 1.
- Factors that can affect test accuracy include certain medications (antidepressants, decongestants), foods (caffeine, vanilla), stress, and improper sample collection or handling.
- If pheochromocytoma is strongly suspected despite negative initial tests, repeated testing or additional imaging studies like CT scans, MRIs, or specialized nuclear medicine scans (MIBG) may be necessary.
- The intermittent nature of hormone secretion and the tumor's ability to sometimes produce minimal amounts of hormones contribute to why these tumors can be considered "the great mimicker" in medicine.
Management and Treatment
- Identifying a single tumor mandates surgical excision after adequate pharmacological preparation, because secreting PPGLs can cause fatal events with no warning 1.
- Administering doxazosin or terazosin, followed by a beta-blocker, usually controls BP and adrenergic crises.
- As PPGLs are associated with a redistribution of volume from the periphery to the cardiopulmonary system, patients with PPGLs have peripheral hypovolaemia that exposes them to the risk of profound hypotension, particularly right after tumor excision. Therefore, adequate fluid administration should be carefully managed 1.
From the Research
Diagnosis of Pheochromocytoma
- Pheochromocytoma can be missed by regular tests if the diagnosis is not suspected and the appropriate screening is not performed 2, 3, 4, 5, 6
- The key to diagnosing pheochromocytoma is to suspect it, then confirm it with biochemical testing and imaging studies 2, 3, 5, 6
- Biochemical testing, such as measurements of plasma free metanephrines, urinary metanephrines, and catecholamines, can confirm the diagnosis of pheochromocytoma in virtually all patients 2, 4, 5
- Imaging studies, such as CT, MRI, and MIBG-scanning, can help to localize the tumor and confirm the diagnosis 2, 3, 5
Limitations of Diagnostic Tests
- False-negative test results can occur in asymptomatic patients or when sampling is carried out between episodes of paroxysmal hypertension 4
- Measurements of urinary total metanephrines or vanillylmandelic acid are less reliable and are of little value as initial screening tests 4
- The relatively low specificity of urinary fractionated metanephrines means that pheochromocytomas can be more efficiently excluded or confirmed using measurements of plasma free metanephrines 4