Distinct sensory and autonomic involvement in hypermobile Ehlers-Danlos syndrome compared with idiopathic small fiber neuropathy: a multimodal study.

Hypermobile Ehlers-Danlos syndrome (hEDS), frequently presents with pain and autonomic symptoms suggestive of small fiber neuropathy (SFN). However, systematic comparisons between hEDS and idiopathic SFN (iSFN) using combined clinical, functional, and morphological approaches are lacking. We prospectively studied a population of SFN patients who also fulfilled the 2017 criteria for hEDS (hEDS/SFN) and compared them with a group of iSFN patients of similar age. All underwent SFN-Symptoms Inventory Questionnaire (SFN-SIQ), Douleur Neuropathique 4 (DN4), and the Composite Autonomic Symptom Score-31 (COMPASS-31) questionnaires, quantitative sensory testing (QST), autonomic testing (cardiovascular reflexes, sympathetic skin response, dynamic sweat test), and skin biopsy from leg, thigh, and fingertip. Clinical, morphological and functional data were compared with our normative dataset and between the two patient groups. 35 hEDS/SFN and 38 iSFN patients were included in the study. hEDS/SFN patients had earlier symptom onset (19.5 ± 5.9 years vs. 35.2 ± 8.7 years, p < 0.001), more generalized distribution, and higher COMPASS-31 scores (54.3 ± 16.9 vs. 33.9 ± 19.4 p < 0.01), particularly in orthostatic intolerance, gastrointestinal, and urinary domains. Postural Orthostatic Tachycardia Syndrome (POTS) was present in half of hEDS/SFN patients while it was not found in iSFN (51.5% vs. 0.0%). Skin biopsy revealed similar intraepidermal nerve fiber loss in both groups, but hEDS had greater autonomic fiber loss (p < 0.05). Small fiber involvement in hEDS is characterized by earlier onset, more generalized pain and severe autonomic symptoms, and higher autonomic morpho-functional impairment compared with iSFN. Systematic autonomic assessment and targeted management should be considered in this population.