The primary objective of this study will be to assess the proportion of fibromyalgia patients with diffuse small-fiber neuropathy (i.e. in the upper and lower limbs) and compare this proportion to patients with other chronic pains (nociplastic, nociceptive) and with healthy controls. Our analysis will be based on the demonstration of structural abnormalities of small nerve fibers by means of skin biopsy, but also of functional abnormalities using four validated tests commonly used in this field: quantitative sensory testing (QST), laser evoked potential recordings, Sudoscan and confocal corneal microscopy. It will thus be possible to verify whether or not patients with small fiber neuropathy have a particular clinical profile in terms of pain, physical activity, comorbidities or pain impact.

Small fiber neuropathy has been observed in a large proportion of fibromyalgia patients. However, the pathophysiological role of these neurological abnormalities in determining the pain and other symptoms of fibromyalgia, and the specificity of these abnormalities, are not well understood.

The primary objective of this study will be to assess the proportion of fibromyalgia patients with diffuse small-fiber neuropathy (i.e. in the upper and lower limbs) and compare this proportion to patients with other chronic pains (nociplastic, nociceptive) and with healthy controls. Our analysis will be based on the demonstration of structural abnormalities of small nerve fibers by means of skin biopsy, but also of functional abnormalities using four validated tests commonly used in this field: quantitative sensory testing (QST), laser evoked potential recordings, Sudoscan and confocal corneal microscopy. It will thus be possible to verify whether or not patients with small fiber neuropathy have a particular clinical profile in terms of pain, physical activity, comorbidities or pain impact.

Inclusion Criteria:

• patients over 18 years of age with no age limit -
• having given their signed consent to take part in the study
• affiliated to the French social security system
• able to be followed for the entire duration of the study
• reading and understanding French
• accepting the principle of the study and able to comply with its conditions
• suffering from chronic pain for at least six months of at least moderate intensity (≥ 4/10)
• fibromyalgia detected by the FiRST questionnare and defined by the revised diagnostic criteria of the WHO or chronic nociceptive or nociplastic pain without associated fibromyalgia.
• chronic pain for at least 6 months of at least moderate intensity (≥ 4/10)
• untreated or with stable analgesic treatment for at least 2 weeks prior to inclusion- normal neurological examination at inclusion

Exclusion Criteria:

• litigation or compensation-seeking
• cancer for less than 2 years
• known cause of small-fiber neuropathy such as diabetes, systemic disease, hypothyroidism, alcohol, renal failure, genetic disease
• clinical or EMG neuropathy
• peripheral or central nervous system pathology with or without associated neuropathic pain
• uncontrolled chronic pathology such as : morbid obesity, sleep apnea, uncontrolled hypertension, etc. - psychosis, previous suicide attempt
• drug or psychoactive substance abuse
• cognitive or psychological disorders incompatible with compliance with and/or understanding of the protocol
• participation in another biomedical research protocol.

Patients with fibromyalgia, other chronic pains (nociplastic or nociceptive) and healthy subjects