Thermal and tactile sensory deficits and allodynia in a nerve-injured patient: a multimodal psychophysical and functional magnetic resonance imaging study.

Objective: A case study was conducted to examine a patient with chronic neuropathic pain of the right foot following peripheral nerve injury and characterize associated sensory abnormalities.

Methods: Multimodal psychophysical examination of the patient's affected and nonaffected foot included thermal sensibility, dynamic touch, and directional sensibility. In addition, we used functional magnetic resonance imaging to study cortical representation of brush-evoked allodynia.

Results: Detailed psychophysical examination revealed substantial deficits in warm, cool, and tactile perception on the injured foot. These findings indicated severe dysfunction of perceptual processes mediated by A beta, A delta, and C fibers. Despite reduced tactile perception, light touch evoked a deep burning pain in the foot. Functional magnetic resonance imaging during brushing of the patient's injured foot showed that tactile allodynia led to activation of several cortical regions including secondary somatosensory cortex, anterior and posterior insular cortex, and anterior cingulate cortex. Brushing of the patient's nonaffected foot led to fewer activated regions.

Discussion: The profound sensory disturbances suggest a possible deafferentation type of tactile allodynia mediated by changes within the central nervous system, such as a disruption of normal tactile or thermal inhibition of nociception. The functional magnetic resonance imaging data suggest that tactile allodynia is represented in similar brain regions as experimental pain.