The aim of the study is to evaluate the interest of the determination of pNFH and NFL neurofilaments in serum for the diagnosis of ALS in patients with a diagnostic standoff after evaluation in an expert ALS center. The hypothesis is that one of these biomarkers, or their combined analysis, will make it possible to confirm or invalidate the diagnosis of ALS.

For this study, which aims to evaluate a test to help in the diagnosis of ALS that could be integrated into routine practice, it was preferred to use blood tests. Blood sampling is significantly less invasive than CSF sampling, and more easily generalized, including in ambulatory conditions.

Inclusion criteria :

Subjects with first and/or second motor neuron disease, evolving clinically and/or electrically over at least 12 months, not meeting the diagnostic criteria for ALS (revised El Escorial criteria):

• Isolated peripheral motor neuron disease (at least one region of the PNM) OR
• Isolated central motor neuron involvement (at least two areas of the MNC) OR
• associated involvement of the MNP and MNC but in the presence of an associated pathology responsible for a persistent diagnostic doubt (double narrow cervical and lumbar canal, associated evolving cancer evoking a paraneoplastic syndrome without specific antibody found) Age superior to 18 years Management and follow-up in one of the French ALS centers Patient able to express his non-opposition Affiliation with social security or beneficiary of such a plan

Non-inclusion criteria:

Refusal of the patient Person under a legal protection measure (guardianship, curatorship or safeguard of justice).

Person deprived of liberty by judicial or administrative decision.

Patients with progressive motor neuron disease without a definite diagnosis.