Morphine consumption is not modified in patients with severe pain and classified by the DN4 score as neuropathic

Abstract

Neuropathic pain has been poorly investigated in the emergency department, although it is known to be less sensitive to opioids than other forms of pain. We tested the hypothesis that morphine requirements are increased in patients having severe pain classified as neuropathic using the DN4 score. We included adult patients with acute severe pain (visual analog scale ≥ 70), assessed using the DN4 score, and treated with intravenous morphine titration (bolus of 2 or 3 mg [body weight >60 kg] with 5-minute intervals between each bolus). Pain relief was defined as a visual analog scale 30 or less. Patients were divided into 2 groups: control group (DN4 score <4) and neuropathic pain group (DN4 score ≥ 4). The main outcome was the total dose of morphine administered. Data are mean ± SD or median (interquartile range). Among the 239 patients included (mean age, 43+14 years), 35 patients (15%) had a DN4 score 4 or more. The main characteristics of the 2 groups were comparable. There were no significant differences between the 2 groups in morphine dose (0.16+0.09 vs 0.17+0.11 mg/kg, P=.32), number of boluses administered (3.5 [3-5] vs 3 [3-6], P=.97), proportion of patients with pain relief (75 vs 83%, P=.39), or morphine-related adverse effects (11% vs 3%, P=.14). In conclusion, morphine consumption was not significantly modified in patients having severe pain classified as neuropathic using the DN4 score as compared with a control group, suggesting that specific detection of neuropathic pain may not be useful in the emergency department.