allodynia

Allodynia is pain that arises from stimuli that would not normally provoke pain in healthy individuals. It is commonly discussed in the context of neuropathic pain and is distinct from hyperalgesia, where a painful stimulus produces an exaggerated pain response. Mechanically induced allodynia refers to pain from light touch or clothing contact, while thermal allodynia involves pain from normally non-painful temperatures. Dynamic allodynia describes pain triggered by light brushing or movement across the skin.

Most allodynia is linked to central sensitization, where the nervous system becomes hyperresponsive after nerve injury or inflammation. Peripheral sensitization at damaged nerves can also contribute. Changes in inhibitory signaling, glial activation, and altered processing of sensory input in the dorsal horn of the spinal cord and higher brain regions can cause non-nociceptive fibers (such as Aβ fibers) to activate pain pathways. Allodynia occurs in a range of conditions, including postherpetic neuralgia, diabetic neuropathy, complex regional pain syndrome, spinal cord injury, multiple sclerosis, and after stroke.

Diagnosis relies on clinical history and examination, supported by quantitative sensory testing in specialized settings. It is important to distinguish allodynia from hyperalgesia and other sources of pain.

Treatment targets both symptoms and underlying causes. Pharmacologic options include anticonvulsants (e.g., gabapentin, pregabalin) and antidepressants (e.g., duloxetine, amitriptyline). Topical therapies such as lidocaine or capsaicin may provide relief for focal allodynia. Nonpharmacologic approaches include physical therapy with graded exposure, psychological therapies, and, in selected cases, neuromodulation (e.g., spinal cord or dorsal root ganglion stimulation). Management is individualized and often requires a multidisciplinary approach.