The effect of interstimulus interval on somatosensory point localization

Upper extremity disability is associated with pain intensity and grip strength in women with bilateral idiopathic carpal tunnel syndrome

BACKGROUND

The upper extremity disability in patients with carpal tunnel syndrome (CTS) is related to dysfunction due to the median nerve damage. However, there is no report on which dysfunctions affect the upper extremity disability.

PURPOSE

This study aimed to investigate which clinical factors influence upper extremity disability in women with CTS.

METHODS

We analyzed 60 hands of women with bilateral idiopathic CTS. Upper extremity disability was assessed using Hand10, a validated and self-administered tool. Pain intensity was measured using the Japanese version of the Short-Form McGill Pain Questionnaire (SF-MPQ-J). We performed nerve conduction studies, assessed physical and psychological parameters, and collected demographic data. Physical parameters comprised grip strength, pinch strength, tactile threshold, static 2-point discrimination sensation, and severity of numbness. Psychological parameters include depression, pain anxiety, and distress.

RESULTS

The bivariate analysis revealed that Hand10 was significantly correlated with age, symptom duration, SF-MPQ-J, grip strength, pain anxiety, and distress. Multiple regression analysis demonstrated that SF-MPQ-J and grip strength were related to Hand10 score.

CONCLUSIONS

Pain intensity and grip strength were dysfunctions affecting the upper extremity disability in women with bilateral idiopathic CTS. Rehabilitation approaches for CTS should be considered based on the adaptive activities of the neural networks.

Sensory capacity of reinnervated skin after redirection of amputated upper limb nerves to the chest

Targeted reinnervation is a new neural-machine interface that has been developed to help improve the function of new-generation prosthetic limbs. Targeted reinnervation is a surgical procedure that takes the nerves that once innervated a severed limb and redirects them to proximal muscle and skin sites. The sensory afferents of the redirected nerves reinnervate the skin overlying the transfer site. This creates a sensory expression of the missing limb in the amputee's reinnervated skin. When these individuals are touched on this reinnervated skin they feel as though they are being touched on their missing limb. Targeted reinnervation takes nerves that once served the hand, a skin region of high functional importance, and redirects them to less functionally relevant skin areas adjacent to the amputation site. In an effort to better understand the sensory capacity of the reinnervated target skin following this procedure, we examined grating orientation thresholds and point localization thresholds on two amputees who had undergone the targeted reinnervation surgery. Grating orientation thresholds and point localization thresholds were also measured on the contralateral normal skin of the targeted reinnervation amputees and on analogous sites in able-bodied controls. Grating orientation thresholds for the reinnervated skin of the targeted reinnervation amputees were found to be similar to normal ranges for both the amputees' contralateral skin and also for the control population. Point localization thresholds for these amputees were found to be lower for their reinnervated skin than for their contralateral skin. Reinnervated point localization thresholds values were also lower in comparison to homologous chest sites on the control population. Mechanisms appear to be in place to maximize re-established touch input in targeted reinnervation amputees. It seems that sound sensory function is provided to the denervated skin of the residual limb when connected to afferent pathways once serving highly functionally relevant regions of the brain. This suggests that tactile interface devices could be used to give a physiologically appropriate sense of touch to a prosthetic limb, which would likely help with better functional utilization of the prosthetic device and possibly help to more effectively integrate the device with the user's self-image.

Localization of touch versus heat pain in the human hand: A dissociative effect of temporal parameters on discriminative capacity and decision strategy

We studied the influence of temporal parameters on localization of monofilament-evoked touch versus thulium laser-induced and C fiber-mediated pain in human subjects. Stimuli were applied at interstimulus intervals (ISIs) varying from 1 to 9 s to determine discrimination between successive stimulus sites in the palmar skin. Localization threshold was about two times higher for heat pain than touch. The localization threshold for pain, but not touch, decreased with prolongation of the ISI from 1 to 7-9 s, and it remained higher for pain even at the ISI of 9 s. The response time was longer for pain than touch, and it increased with an increase in the ISI, independent of the modality. Discriminative capacity, as assessed by the receiver operating characteristics curve, was markedly better for touch than pain. The discriminative capacity decreased with an increase of the ISI, but only for touch. The results indicate that localization is more accurate for touch than pain. Temporal summation of C fiber-evoked pain contributes to the reduced accuracy of pain localization if the ISI is < or = 3 s. Additionally, temporal factors dissociatively influence the response strategy in the tactile versus pain localization task with the prolongation of the ISI from 1 to 9 s. Due to this strategy change, localization threshold for touch remains constant at prolonged ISIs, in spite of a decrease in discriminative capacity. In a cutaneous localization task, the subject's accuracy and response strategy vary with the modality and temporal parameters of sequential test stimulation.