False-positive results for pheochromocytoma associated with norepinephrine reuptake blockade

Measurements of plasma metanephrines and methoxytyramine provide a sensitive test for diagnosis of pheochromocytoma/paraganglioma. False-positive results remain a problem, particularly in patients taking norepinephrine reuptake-blocking drugs. Therefore, in this retrospective observational study, we measured plasma metanephrines and methoxytyramine in 61 patients taking norepinephrine reuptake blockers (tricyclic antidepressants or serotonin-norepinephrine reuptake inhibitors) and 17 others taking selective serotonin reuptake inhibitors, all without pheochromocytoma/paraganglioma. We highlight a singular case with strongly elevated plasma normetanephrine and methoxytyramine concentrations associated with norepinephrine reuptake blockade. Data were compared to results from 252 and 1804 respective patients with and without tumors. Plasma normetanephrine was 40% higher (P < 0.0001) in patients on norepinephrine reuptake blockers and methoxytyramine was 127% higher (P = 0.0062) in patients taking tricyclic antidepressants compared to patients not taking uptake blockers and without tumors. The corresponding false-positive rates rose (P < 0.0001) from 4.8% to 23.0% for normetanephrine and from 0.9% to 28.6% for methoxytyramine. Selective serotonin reuptake inhibitors did not increase plasma concentrations of metabolites. In the highlighted case, plasma normetanephrine and methoxytyramine were elevated more than six times above upper reference limits. A pheochromocytoma/paraganglioma, however, was excluded by functional imaging. All biochemical test results normalized after discontinuation of norepinephrine reuptake blockers. These findings clarify that norepinephrine reuptake blockers usually result in mild elevations of normetanephrine and methoxytyramine that, nevertheless, significantly increase the number of false-positive results. There can, however, be exceptions where increases in normetanephrine and methoxytyramine reach pathological levels. Such exceptions may reflect failure of centrally mediated sympathoinhibition that normally occurs with the norepinephrine reuptake blockade.

Efficacy of venlafaxine extended release in major depressive disorder patients: effect of baseline anxiety symptom severity

Effects of baseline anxiety on the efficacy of venlafaxine extended release versus placebo were examined in a post hoc pooled subgroup analysis of 1573 patients enrolled in eight short-term studies of major depressive disorder. Anxiety subgroups were defined based on baseline 17-item Hamilton Rating Scale for Depression Item 10 score <3 (low) versus ≥3 (high). Change from baseline to final visit in Montgomery-Åsberg Depression Rating Scale total score and Montgomery-Åsberg Depression Rating Scale response and remission rates were analyzed. Change from baseline in Montgomery-Åsberg Depression Rating Scale total score and response and remission rates was significantly greater for venlafaxine extended release versus placebo in both low and high anxiety subgroups (all P < 0.0001). A statistically significant baseline anxiety by treatment interaction was observed for Montgomery-Åsberg Depression Rating Scale total score only (P = 0.0152). The adjusted mean change from baseline in Montgomery-Åsberg Depression Rating Scale total score was significantly greater in the high anxiety subgroup versus low anxiety subgroup for patients treated with venlafaxine extended release (-6.27 versus -3.89; P = 0.0440) but not placebo. These results support the efficacy of venlafaxine extended release for major depressive disorder treatment in patients with anxiety symptoms.