Allodynia

Allodynia refers to pain caused by what would normally be non-painful stimulation, for example brushing the skin. Temperature change, light touching, and clothing can trigger the pain response resulting in a burning sensation often occurring after an injury to a site.

Presentation
There are three types of allodynia:
 * Tactile, where pain is caused by touches such as clothing touching the skin or someone lightly touching the arm;
 * Mechanical, caused by movement across the skin when drying with a towel or sheets brushing against the skin; and
 * Thermal, which is caused by heat or cold that is not extreme enough to cause damage to skin tissues.

Allodynia in ME/CFS and Fibromyalgia
Allodynia is not a diagnostic symptom of ME or CFS, although pain in general is. Allodynia is not directly mentioned in the International Consensus Criteria primer for Myalgic Encephalomyelitis but would fulfill the significant pain diagnostic criteria, which includes a number of types of pain including hyperalgesia and widespread pain that may meet the fibromyalgia criteria.

Prevalence
A study of over 3,000 patients with fibromyalgia found that allodynia was "surprisingly common."

Notable studies

 * 2009, Models and Mechanisms of Hyperalgesia and Allodynia (Full text)
 * 2010, A cross-sectional survey of 3035 patients with fibromyalgia: subgroups of patients with typical comorbidities and sensory symptom profiles (Full text)

Possible causes
Central pain sensitization (increased response of neurons) has been proposed as a possible cause, but this term has conflicting definitions and scientific evidence is unclear.

Learn more

 * Pain terminology - International Association for the Study of Pain