Phaeochromocytoma without hypertension
A 34 year old woman presented with a 10 week history of paroxysmal attacks of headache associated with vomiting, sweating,and palpitations. Her blood pressure always remained normal during these episodes. A 24 hour urine collection showed a mildly elevated level of adrenaline at 180 nmol/24hr (normal < 140nmol/24hr) with normal levels of noradrenaline and dopamine. Abdominal computed tomography (CT) showed the following abnormality (see figure).
To screen for phaeochromocytoma, 24 hour urinary excretory rates of catecholamines and their metabolites--for example, norepinephrine, epinephrine, dopamine, metanephrine, normetanephrine--are useful. These measurements provide close to 100% specificity and sensitivity in diagnosing the condition. CT, magnetic resonance imaging (MRI), and scanning with iodine-131-meta-iodobenzylguanidine (MIBG) are commonly used in localising the tumour. The specificity of a MIBG scan approaches 100% (making it very useful for extra-adrenal lesions), but its sensitivity is only 80%.4 CT and MRI scans have a sensitivity of 98% to 100% but a