Is there pain with neuropathic characteristics in patients with amyotrophic lateral sclerosis? A cross-sectional study

Abstract

Even if amyotrophic lateral sclerosis is a disease of the motor system, pain is frequent and can rarely have neuropathic characteristics. Pain must be always sought and appropriately treated to limit quality of life impairment.

Pain in amyotrophic lateral sclerosis

“…10,11 Pain was quite a neglected symptom in ALS up until about ten years ago 12 owing to a misconception of the disease as purely of a motor nature, that leads clinicians not to ask their patients about pain, 12,13 as also has been the case with other non-motor symptoms. However, in the last decade, the variability of ALS between affected individuals has clearly emerged, and among the wide spectrum of neurological defects and adjunctive manifestations that have been investigated, several studies have focused on pain in ALS, [13][14][15][16][17][18] confirming earlier observations. [19][20][21] Furthermore, pain has been considered, mostly from a therapeutic point of view, in the main guidelines of ALS treatment, 22,23 being also the subject of a Cochrane review.…”

“…74 This approach, however, has not been systematically used for the assessment of neuropathic pain in ALS. Indeed, two clinical studies that have investigated the neuropathic origin of pain in ALS patients using questionnaires that can be used as discriminative or descriptive instruments, either did not find evidence for neuropathic pain 25 or identified only a minority of patients with features of neuropathic pain (i.e., numbness, burning, tingling, etc, 40 but did not confirm findings in these patients with nerve conduction studies or skin biopsies.…”

“…However, two clinical studies on neuropathic pain in ALS provide no or only weak evidence for this pain type in patients with ALS: in a case-control study, no patients scored high enough in the Pain Detect Questionnaire to reach the neuropathic threshold, and 80% of ALS patients scored less than 12/38, suggesting that their pain was nociceptive in nature, 25 while a cross-sectional study showed that only 9% of 96 patients with pain had features of neuropathic pain according to the Neuropathic Pain Diagnostic Questionnaire and higher pain intensity score. 40 Spasticity and cramps are other common primary causes of pain in ALS. Cramps are the major cause of pain in about one-quarter of patients, mainly with the spinal form.…”

“…31 In keeping with these findings, one study demonstrated that pain intensity did not correlate with the Pain Interference Score, 17 suggesting that pain itself, but not its severity, may be a major determinant of suffering in ALS patients. However, more than 50% of ALS patients complaining of pain were reported to use pain drugs 14,17,25,30,40,46 more frequently than population-based controls, indicating that when pain is detected in ALS patients is more likely to be actively treated than in the general population. 14…”

“…25 Moreover, the hypothesis that pain in ALS may be caused by the reduced mobility should suggest a correlation with the duration of the disease that, however, is still a controversial issue. 14,15,17,40,79 Therefore, although some patients with evidence of tissue or joint damage can be definitely diagnosed with nociceptive pain, others might acquire an enhanced sensory response to normal inputs normally evoking innocuous sensations driven by central sensitization. Two definitions are currently recognised: an amplification of neural signalling within the central nervous system that elicits pain hypersensitivity 72 and an augmented responsiveness of central nervous system (CNS) neurons to normal or subthreshold afferent inputs that evoke innocuous sensations.…”