Sensory correlates of pain in peripheral neuropathies

To characterize sensory threshold alterations in peripheral neuropathies and the relationship between these alterations and the presence of pain.

Seventy-four patients with length-dependent sensory axonal neuropathy were enrolled, including 38 patients with painful neuropathy (complaining of chronic, spontaneous neuropathic pain in the feet) and 36 patients with painless neuropathy. They were compared to 28 age-matched normal controls. A standardized quantitative sensory testing protocol was performed in all individuals to assess large and small fiber function at the foot. Large fibers were assessed by measuring mechanical (pressure and vibration) detection thresholds and small fibers by measuring pain and thermal detection thresholds.

Between patients with neuropathy and controls, significant differences were found for mechanical and thermal detection thresholds but not for pain thresholds. Patients with painful neuropathy and those with painless neuropathy did not differ regarding mechanical or thermal thresholds, but only by a higher incidence of thermal or dynamic mechanical allodynia in case of painful neuropathy. Pain intensity correlated with the alteration of thermal detection and mechanical pain thresholds.

Quantitative sensory testing can support the diagnosis of sensory neuropathy when considering detection threshold measurement. Thermal threshold deterioration was not associated with the occurrence of pain but with its intensity.

There is a complex relationship between the loss or functional deficit of large and especially small sensory nerve fibers and the development of pain in peripheral neuropathy.