Central sensitization in carpal tunnel syndrome with extraterritorial spread of sensory symptoms

Abstract

Extraterritorial spread of sensory symptoms is frequent in carpal tunnel syndrome (CTS). Animal models suggest that this phenomenon may depend on central sensitization. We sought to obtain psychophysical evidence of sensitization in CTS with extraterritorial symptoms spread. We recruited 100 unilateral CTS patients. After selection to rule out concomitant upper-limb causes of pain, 48 patients were included. The hand symptoms distribution was graded with a diagram into median and extramedian pattern. Patients were asked on proximal pain. Quantitative sensory testing (QST) was performed in the territory of injured median nerve and in extramedian territories to document signs of sensitization (hyperalgesia, allodynia, wind-up). Extramedian pattern and proximal pain were found in 33.3% and 37.5% of patients, respectively. The QST profile associated with extramedian pattern includes: (1) thermal and mechanic hyperalgesia in the territory of the injured median nerve and in those of the uninjured ulnar and radial nerves and (2) enhanced wind-up. No signs of sensitization were found in patients with the median distribution and those with proximal symptoms. Different mechanisms may underlie hand extramedian and proximal spread of symptoms, respectively. Extramedian spread of symptoms in the hand may be secondary to spinal sensitization but peripheral and supraspinal mechanisms may contribute. Proximal spread may represent referred pain. Central sensitization may be secondary to abnormal activity in the median nerve afferents or the consequence of a predisposing trait. Our data may explain the persistence of sensory symptoms after median nerve surgical release and the presence of non-anatomical sensory patterns in neuropathic pain.

Ultrasonographic assessment of the shoulder in patients with carpal tunnel syndrome

“…The pain was found commonly and more severe in patients with mild CTS [5,6]. In our study, the severity of CTS had no correlation with proximal spread, shoulder pain, or shoulder ultrasonographic evaluation.…”

“…These authors suggested that the continuous sensory bombardment from the median nerve might trigger cortical plastic changes. In another study, Zanette et al, (6) did not find association between proximal pain and central sensitization. They hypothesized that proximal pain may represent referred pain and activation of specific A delta and C-fibre populations may cause proximal spread in CTS.…”

“…Apart from the rotator cuff problems, extramedian and proximal pain in CTS patients also can be associated with central sensitization and plasticity which was demonstrated by recent studies [5,6,20]. Central sensitization can be defined as an increased pain response of the central nervous system after nociceptive stimulation.…”

“…This phenomenon has contributed to central sensitization [3][4][5][6]. Additionally, patients with CTS complain shoulder pain frequently [5,6]. In a study, proximal pain was found 45% in CTS [5], in another study 21% of patients had forearm pain, 13.8% elbow pain, 7.5% arm pain, 6.3% shoulder pain and 0.6% neck pain [7].…”

“…Many studies have reported that the pain spread to extramedian areas and proximal part of the upper extremity. This phenomenon has contributed to central sensitization [3][4][5][6]. Additionally, patients with CTS complain shoulder pain frequently [5,6].…”