The evaluation of pain during botulinum toxin (BT) injections has never been conducted in adults. Our main objective was to quantified pain perceived by individuals with a stroke, during BT injections. A second objective was to analyze clinical and technical determinants of a painful procedure.

Observational study on 46 persons (19M/27W, 60.5±16 years) evaluated without analgesia during injections of BT-A performed by 2 experts (15 years of experience each), 6.5 years after a stroke. Pain was evaluated by numeric verbal scale (0–10) after each step. Pressure hypoesthesia was assessed by Semmes–Weinstein monofilaments. The existence of chronic pain was established from a long-term intake of antalgic drugs. Following are presented in median [25 and 75th percentiles].

A total of 1288 numerical verbal scale results were analyzed. The most painful time was stimulation (4 [2.6–5.3]; P<0.001) followed by needle insertion (3.1 [1.3–4.1]; P<0.01). Pain resulting from toxin injection was not negligible (1 [0.1–2.3]; P<0.01), over pain resulting from needle withdrawal (0 [0–0.3]; P<0.05). Pain perceived during stimulation was inversely correlated with hypoesthesia (P<0.02) Patients who suffered from chronic pain perceived a greater pain during puncture and stimulation (P<0.05). Pain was not influenced by age, time duration since stroke, stroke side, number of muscle's injections per session. Pain was positively correlated with the needle's length, for puncture (r=0.3, P=0.01) and the withdrawal (r=0.4, P=0.009). The needle's brand also influenced pain during puncture (P=0.01). Pain was not influenced by the dose or the volume injected, neither by the product used.

Botulinum Toxin injection is a very painful act which imposes a rigorous pain prevention. Suppressing the stimulation does not suppress pain. Patients at risk for pain should be identified, and the procedure adapted.