Emerging Role of Liquid Chromatography–Mass Spectrometry in the Clinical Laboratory Evaluation of Chronic Autonomic Failure
Emerging Role of Liquid Chromatography–Mass Spectrometry in the Clinical Laboratory Evaluation of Chronic Autonomic Failure
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Original abstract
ABSTRACT 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 18 F‐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 18 F‐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. image