Pain
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Randomized Controlled Trial
Repeated intramuscular injections of nerve growth factor induced progressive muscle hyperalgesia, facilitated temporal summation, and expanded pain areas.
Intramuscular injection of nerve growth factor (NGF) is known to induce deep-tissue mechanical hyperalgesia. In this study it was hypothesised that daily intramuscular injections of NGF produce a progressive manifestation of soreness, mechanical hyperalgesia, and temporal summation of pain. In a double-blind placebo-controlled design, 12 healthy subjects were injected on 3 days with NGF into the tibialis anterior muscle and with isotonic saline on the contralateral side. ⋯ Compared with baseline and isotonic saline, the NGF injections caused (P<0.05): (1) progressively increasing soreness scores from 3 hours after the first injection until day 2, after which it remained increased; (2) decreased PPTs at days 1 to 3; (3) facilitated temporal summation of pressure pain at days 1 to 10; and (4) enlarged pressure-induced pain area after the injection on day 1 to day 6. The daily injections of NGF produced a progressive manifestation of muscle soreness, mechanical hyperalgesia, temporal summation of pressure pain, and pressure-induced pain distribution. These data illustrate that the prolonged NGF application affects peripheral and central mechanisms and may reflect process in musculoskeletal pain conditions.