Novel adaptations in motor cortical maps: the relation to persistent elbow pain.

Abstract

Unilateral elbow pain results in sensorimotor dysfunction that is frequently bilateral, affects local and remote upper limb muscles, and persists beyond resolution of local tendon symptoms. These characteristics suggest supraspinal involvement. Here, we investigated 1) the excitability and organization of the M1 representation of the wrist extensor muscles and 2) the relation between M1 changes and clinical outcomes in lateral epicondylalgia (LE) (n = 11) and healthy control subjects (n = 11). Transcranial magnetic stimulation was used to map the M1 representation of the extensor carpi radialis brevis (ECRB) and extensor digitorum (ED). The cortical representations of ECRB and ED were more excitable, and the centers of gravity for the two muscles were located closer together in LE than that in healthy controls. Increased ECRB excitability and closer location of the center of gravity were associated with higher pain severity at rest and/or in the preceding 6 months. A novel finding was a reduced number of discrete peaks in the representations of ECRB and ED in participants with LE compared with that in healthy controls. This finding may have broad implications for the control of the wrist extensor muscles in LE. These data provide evidence that cortical organization may be maladaptive in LE and suggest that reorganization may be associated with persistence/recurrence of pain.