Dopamine concentration in blood platelets is elevated in patients with head and neck paragangliomas.

BACKGROUND Plasma 3-methoxytyramine (3-MT), a metabolite of dopamine, is elevated in up to 28% of patients with head and neck paragangliomas (HNPGLs). As free dopamine is incorporated in circulating platelets, we determined dopamine concentration in platelets in patients with a HNPGL. METHODS A single center cohort study was performed between 2012 and 2014. Thirty-six patients with a HNPGL were compared to healthy controls (68 for dopamine in platelets and 120 for plasma 3-MT). RESULTS Dopamine concentration in platelets was elevated in HNPGL patients compared to healthy controls (median [interquartile ranges] 0.48 [0.32-0.82] pmol/109 platelets vs. 0.31 [0.24-0.47] pmol/109 platelets; p<0.05), whereas plasma 3-MT concentration did not differ between both groups (0.06 [0.06-0.08] nmol/L vs. 0.06 [0.06-0.06] nmol/L; p=0.119). Based on 68 healthy controls, the reference interval for dopamine concentration in platelets was 0.12-0.97 pmol/109 platelets. Six (16.7%) patients with a HNPGL demonstrated an increased dopamine concentration in platelets compared to three (8.3%) patients with an increased plasma 3-MT level (p=0.053). The sensitivity and specificity were 16.7% and 98.5% for platelet dopamine and 8.3% and 97.5% for plasma 3-MT concentration (p=0.37). CONCLUSIONS Dopamine concentration in platelets is elevated in patients with a HNPGL compared to healthy subjects, and may be a novel biomarker for dopamine producing paraganglioma.