Diagnosis of atypic pheochromocytomas: a challenge also for biologists

Biological diagnosis of pheochromocytoma is relatively easy in those cases releasing great amounts of catecholamines with strong clinical features; in stead, diagnosis could be more problematic in atypical or asymptomatic fami lial pheochromocytoma with small tumors secreting low catecholamine amounts . Several plasma and urine adrenergic markers must be used to confirm the c linical suspicion. We have discussed the biological data of three totally a symptomatic pheochromocytomas (cases n(o)2, 3, 4) and one case with a very discrete clinical manifestation (n(o) 1). Three patients had very small tum ors (4, 7 and 25 g) secreting preeminently adrenaline, one patient had a 45 g adrenal incidentaloma without clinical expression. Our study shows that, in these special cases, except an unconstant increase of adrenaline, plasm a and urine catecholamines and urine VMA can be normal. The most useful mar kers are plasma and urine methoxyamines. However, plasma methoxyamines are the most sensitive because their increase over reference values is by far g reater than in urines. Several factors may explain these findings: a low tu moral secretion, the nature of the released amine, the short half-life of c atecholamines in plasma and, in some cases, the involvement of intratumoral catecholamine metabolism. Analysis of the ratio NMN/MN in plasma provides an additional diagnosis tool to reveal adrenaline secretion abnormalities. (C) 2001 Editions scientifiques et medicales Elsevier SAS.