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Delayed diagnosis and misdiagnosis are frequent in people with amyotrophic lateral sclerosis (ALS), the most common form of motor neuron disease (MND). Neurofilament light chain (NFL) and phosphorylated neurofilament heavy chain (pNFH) are elevated in ALS patients. We retrospectively quantified cerebrospinal fluid (CSF) NFL, CSF pNFH and plasma NFL in stored samples that were collected at the diagnostic work-up of ALS patients (n = 234), ALS mimics (n = 44) and controls (n = 9). We assessed the diagnostic performance, prognostication value and relationship to the site of onset and genotype. CSF NFL, CSF pNFH and plasma NFL levels were significantly increased in ALS patients compared to patients with neuropathies & myelopathies, patients with myopathies and controls. Furthermore, CSF pNFH and plasma NFL levels were significantly higher in ALS patients than in patients with other MNDs. Bulbar onset ALS patients had significantly higher plasma NFL levels than spinal onset ALS patients. ALS patients with C9orf72HRE mutations had significantly higher plasma NFL levels than patients with SOD1 mutations. Survival was negatively correlated with all three biomarkers. Receiver operating characteristics showed the highest area under the curve for CSF pNFH for differentiating ALS from ALS mimics and for plasma NFL for estimating ALS short and long survival. All three biomarkers have diagnostic value in differentiating ALS from clinically relevant ALS mimics. Plasma NFL levels can be used to differentiate between clinical and genetic ALS subgroups.

Purpose: To investigate changes in myofiber composition in the global layer (GL) and orbital layer (OL) of extraocular muscles (EOMs) from terminal amyotrophic lateral sclerosis (ALS) donors.

Methods: Medial recti muscles collected postmortem from spinal-onset ALS, bulbar-onset ALS, and healthy control donors were processed for immunofluorescence with antibodies against myosin heavy chain (MyHC) IIa, MyHCI, MyHCeom, laminin, neurofilaments, synaptophysin, acetylcholine receptor γ-subunit, and α-bungarotoxin.

Results: The proportion of myofibers containing MyHCIIa was significantly smaller and MyHCeom was significantly larger in the GL of spinal-onset ALS and bulbar-onset ALS donors compared to control donors. Changes in the GL were more prominent in the bulbar-onset ALS donors, with a significantly larger proportion of myofibers containing MyHCeom being present compared to spinal-onset ALS donors. There were no significant differences in the myofiber composition in the OL. In the spinal-onset ALS donors, the proportions of myofibers containing MyHCIIa in the GL and MyHCeom in the OL were significantly correlated with the disease duration. Neurofilament and synaptophysin were present at motor endplates of myofibers containing MyHCeom in ALS donors.

Conclusions: The EOMs of terminal ALS donors displayed changes in the fast-type myofiber composition in the GL, with a more pronounced alteration in bulbar-onset ALS donors. Our results align with the worse prognosis and subclinical changes in eye movement function previously observed in bulbar-onset ALS patients and suggest that the myofibers in the OL might be more resistant to the pathological process in ALS.