Serum and cerebrospinal fluid phosphorylated neurofilament heavy protein concentrations in equine neurodegenerative diseases

Background Currently, there is little information regarding the concentrations of phosphorylated neurofilament heavy protein (pNfH) in the serum and cerebrospinal fluid (CSF) of horses with neurodegenerative diseases. Specifically, pNfH concentrations have not yet been evaluated in horses with equine neuroaxonal dystrophy/equine degenerative myeloencephalopathy (eNAD/EDM). Objectives To determine pNfH concentrations using a commercial enzyme-linked immunosorbent assay (ELISA) in serum and CSF from control horses and horses with eNAD/EDM, cervical vertebral compressive myelopathy (CVCM) and Shivers. Study design Case-control study using biobanked samples from diseased horses and prospective or biobanked samples from control horses. Methods The pNfH ELISA was performed on samples from horses diagnosed with eNAD/EDM (n = 64), CVCM (n = 26) and Shivers (n = 9) and 51 neurologically normal control horses. Results Median and 95% confidence interval (CI) serum pNfH concentrations in control, CVCM, and eNAD/EDM horses were 0.08 ng/mL (0.07-0.15), 0.07 ng/mL (0.07-0.15) and 0.07 ng/mL (0.07-1.13), respectively. Serum pNfH concentrations were below the limit of detection (<0.07 ng/mL) for all Shivers horses. CSF pNfH concentrations in control, CVCM-, eNAD/EDM- and Shivers-affected horses were 1.26 ng/mL (1.06-1.5), 3.07 ng/mL (1.15-29.9), 1.78 ng/mL (1.5-2.28) and 1.39 ng/mL (0.74-3.89), respectively. CSF pNfH concentrations were significantly higher in CVCM (P = .001) and eNAD/EDM (P = .01) affected horses compared to control horses. Serum pNfH concentrations >1 ng/mL were significantly associated with eNAD/EDM (P = .01) with only 12% sensitivity but 99% specificity. CSF pNfH concentrations >3 ng/mL were significantly associated with CVCM (P = .0002), with 50% sensitivity and 86% specificity. Main limitations A limited number of control horses tested were Serum pNfH concentrations are specifically increased (>1 ng/mL) in some horses with eNAD/EDM. Increased CSF pNfH concentrations (>3 ng/mL) can be observed with eNAD/EDM or CVCM.