Abnormal capacity for grip force control in patients with congenital insensitivity to pain

Congenital insensitivity to pain (CIP), which is an extremely rare sensory neuropathy, is defined as the absence of normal responses to noxious stimuli. Although motor function is not directly impaired in CIP patients, it is likely that the sensory deficit affects the motor control system. In order to characterize motor capacity in CIP patients, we here measured grip force and acceleration of a held object in 12 patients with CIP and 12 age-matched able-bodied subjects. The results demonstrated that the grip force during the object grasp-lift-holding task was significantly greater, less reproducibility and greater fluctuation in the acceleration of the object in CIP patients than in normal subjects. Moreover, some patients showed absence of temporal coupling between the grip and load force, suggesting that anticipatory modulation of the grip force was at least partly impaired. As far as the authors know, this is the first study to characterize motor control ability in patients with CIP. The observed abnormal motor capacity can be at least partly attributed to a lack of sensory inputs mediated by Aδ and unmyelinated C-, specifically C-tactile, fibers. The present results may provide information useful for the prevention of secondary injury and education for patients during the developmental stage.