Hypermobility, the Ehlers-Danlos syndromes and chronic pain.

Chronic widespread pain is a common complaint among individuals affected by generalised joint hypermobility. In the absence of other conditions that cause chronic pain, these individuals are usually diagnosed with joint hypermobility syndrome (JHS). JHS is a multifactorial trait with a strong genetic basis, but no specific genetic markers. Clinical overlap of JHS is seen with heritable connective tissue disorders, particularly with the Ehlers-Danlos syndrome, hypermobile type (hEDS). The Ehlers-Danlos syndromes (EDS) comprise a heterogeneous group of rare monogenic conditions that are characterised by joint hypermobility, skin and vascular fragility and generalised connective tissue friability, and are caused by genetic defects in an array of extracellular matrix genes. The genetic basis of hEDS remains however unknown, in contrast to other well-described EDS subtypes. In view of the considerable clinical overlap with JHS, many consider it and hEDS to be a single clinical entity. Clinical experience and a limited number of clinical studies show that chronic pain also is common in EDS patients, especially in hEDS. The specific underlying causes and mechanisms of pain in JHS and EDS remain poorly understood. Factors likely contributing to the generation and chronicity of pain include nociceptive pain, directly based on structural changes in affected joints, muscle and connective tissue; neuropathic pain; impaired proprioception and muscle weakness; and central sensitisation. These mechanisms are not mutually exclusive, and likely more than one mechanism may be present. Furthermore, anxiety, depression, and other variables may influence the phenotype. Chronic pain in JHS and EDS patients often is inadequately controlled by traditional analgesics and physical therapy. In view of the high prevalence of these underrecognised conditions, future studies addressing the nature and mediators of chronic pain are needed in order to potentially identify novel targets for therapeutic intervention and optimise treatment.