Emerging Role of Liquid Chromatography-Mass Spectrometry in the Clinical Laboratory Evaluation of Chronic Autonomic...

Liquid chromatography with electrochemical detection (LC-ED) after batch alumina extraction has been the mainstay for assaying levels of catecholamines and related 3,4-dihydroxy compounds (catechols) as part of the clinical laboratory workup of patients with neurogenic orthostatic hypotension, especially in the setting of the autonomic synucleinopathies Parkinson disease with orthostatic hypotension (PD + OH), pure autonomic failure (PAF), and multiple system atrophy (MSA). Liquid chromatography with tandem mass spectrometry (LC-MS/MS) is faster and measures catechols and non-catechol metabolites simultaneously but has not yet been validated sufficiently against LC-ED or used to assess catechol vs. non-catechol neurochemical abnormalities in autonomic synucleinopathies. We measured plasma catechols by LC-MS/MS and LC-ED in patients with PAF, PD + OH, or MSA and healthy controls. Cardiac sympathetic neuroimaging by ¹⁸F-dopamine positron emission tomography (PET) was used to indicate myocardial norepinephrine (NE) content in the same subjects. Across 41 participants (12 PAF, 9 PD + OH, 10 MSA, 10 controls) individual values for plasma 3,4-dihydroxyphenylglycol (DHPG), NE, and 3,4-dihydroxyphenylalanine (DOPA) by LC-MS/MS correlated positively with values by LC-ED (r = 0.97, 0.98, and 1.00, p < 0.0001 each). The PAF group had low mean NE, DHPG, normetanephrine, 3-methoxy-4-hydroxyphenylglycol, epinephrine, and metanephrine compared to the PD + OH group, while cardiac PET did not separate the 2 groups. We therefore conclude that LC-MS/MS validly assays plasma catechols. Several catechol and non-catechol biomarkers of generalized catecholamine deficiency separate PAF from PD + OH but not PD + OH from MSA, while ¹⁸F-dopamine PET separates PAF and PD + OH from MSA but not PAF from PD + OH. Combining LC-MS/MS with cardiac sympathetic neuroimaging efficiently differentiates among these conditions.