Chronic Cough and Small Fiber Neuropathy

Diabetic patients with and without chronic cough will be included in this study. After giving their informed consent, the patients will perform a spirometry, chest X-ray at the inclusion visit. Cough will be assessed using the cough visual analog scale (VAS) and the Leicester Cough Questionnaire (LCQ). Within 60 days, the patient will perform neurophysiological tests. The neurophysiological assessment will be concluded with a skin biopsy to evaluate small fiber neuropathy. The aim of the study is to compare the proportion of small fiber neuropathy between diabetic patients with chronic cough and those without chronic cough.

Chronic cough is a very common entity that affects 9.6% people worldwide. Given the high number of patients with refractory cough, the concept of cough hypersensitivity syndrome (CHS) has emerged. In CHS, afferent sensory nerves may exhibit a modification of activation patterns with facilitation of encoding signals in response to irritating stimuli. Similar patterns with neuropathic pain have been described. Small fiber neuropathy has never been assessed in chronic cough. Interestingly, diabetic patients experienced cough more frequently than healthy subject. We hypothesized that small fiber neuropathy may explain chronic cough is more frequent in diabetic patients.

Within 60 days after inclusion, diabetic patients with and without chronic cough will perform neurophysiological tests such as electromyography, thermotest, QSART (Quantitative Sudomotor Axon Reflex Test and Sudoscan), cardio-vascular tests to study the autonomic nervous system. No risks are expecting with these non-invasive tests. A skin biopsy to evaluate small fiber neuropathy will also be performed.After the neurophysiological tests, a consultation will be scheduled at 6 months. A cough VAS and LCQ will be used to assess cough.

Eligibility Criteria:
Inclusion Criteria:

In diabetic patients with chronic cough:

* Chronic cough defined by cough for more than 8 weeks.
* Normal chest X-ray
* history of type 2 diabetes
* Age of diabetes onset\> 40 years
* Affiliated or beneficiary person of social security
* Free, informed and written consent

In diabetic patients without chronic cough

* History of type 2 diabetes
* Age of discovery of diabetes\> 40 years
* Affiliated or beneficiary person of social security
* Free, informed and written consent

Exclusion Criteria:

* Presence of physical signs of peripheral neuropathy
* Active smoking or smoking cessation within the last 12 months
* Pregnant or lactating woman
* History of non-type 2 diabetes (type I, secondary diabetes, monogenic ...)
* Cancer within the last 5 years (except cutaneous squamous cell carcinoma)
* History of anti-cancer chemotherapy
* Suspicion of autoimmune pathology
* Active neurological pathology
* Electromyography in favor of large fiber neuropathy
* Chronic pathology that may interfere with the neurophysiological assessment
* Patient who were given anticoagulation drug therapy, anti-cholinergic drugs, beta-blocker and impossibility to withdraw the treatment before neurophysiological tests

In diabetic patients without chronic cough, another non-inclusion criteria is acute or chronic cough