Expert Panel: Dominic Chamberlain, Future Medicine Ltd, London, UK
Haroutiunian S, Nikolajsen L, Bendtsen TF et al. Primary afferent input critical for maintaining spontaneous pain in peripheral neuropathy. Pain doi:10.1016/j.pain.2014.03.022 (2014) (Epub ahead of print).
In this study the authors used peripheral nerve blockade and systemic lidocaine administration, with detailed somatosensory assessment, to determine the contribution of primary afferent input in maintaining peripheral neuropathic pain. A total of 14 patients with neuropathic pain underwent comprehensive characterization of somatosensory function by quantitative sensory testing. The team then administered an ultrasound-guided peripheral nerve block with lidocaine and intravenous lidocaine infusion in randomized order, and assessed the effect of these interventions on spontaneous pain intensity and on evoked cold, warm, pinprick, and brush responses. The authors report that the peripheral nerve block resulted in a complete abolition of ipsilateral pain within 10 min in all patients with lidocaine plasma concentrations being too low to account for a systemic effect of the drug. Intravenous lidocaine infusion reduced the spontaneous pain by 45.5% (± 31.7%), and reduced mechanical and thermal hypersensitivity in most patients who displayed such signs, but the improvement in evoked hypersensitivity was not related to the effect of the drug on spontaneous pain intensity. The authors argue that the study demonstrates that regardless of the individual somatosensory phenotype and signs of central sensitization, primary afferent input is critical for maintaining neuropathic pain in peripheral nerve injury and distal polyneuropathy.
Knauf M, Koltyn K. Exercise-induced modulation of pain in adults with and without painful diabetic neuropathy. J. Pain doi:10.1016/j.jpain.2014.02.008. (2014)(Epub ahead of print).
In this study the authors aimed to examine exercise-induced pain modulation in diabetic adults with painful diabetic neuropathy (PDN) compared with diabetic adults without PDN. A total of 18 adults diagnosed with Type 2 diabetes with and without PDN completed two sessions. In the first session participants completed questionnaires, were familiarized with the pain testing protocols and completed maximal isometric contractions. During the second session, experimental pain testing was completed before and following exercise consisting of three minutes of isometric exercise. The authors assessed ratings of perceived exertion and muscle pain every 30 s during exercise. The results indicated that ratings of perceived exertion and muscle pain during exercise were significantly higher for diabetic adults with PDN versus diabetic adults without PDN. Diabetic adults with PDN did not experience changes in thermal pain ratings following exercise while diabetic adults without PDN reported significantly lower pain ratings following exercise. The team conclude that that diabetic adults with PDN experience high levels of muscle pain during exercise and a lack of exercise-induced hypoalgesia following exercise in comparison to diabetic adults without PDN, who experience lower levels of muscle pain during exercise and a hypoalgesic response following exercise.
Valentini E, Martini M, Lee M, Aglioti S, Iannetti G. Seeing facial expressions enhances placebo analgesia. Pain doi:10.1016/j.pain.2013.11.021 (2014) (Epub ahead of print).
In this study the authors aimed to assess whether the observation of facial expressions with different emotional content affects the magnitude of placebo analgesia, and whether interindividual differences in personality traits interact with any modulation of placebo response induced by facial expression.
In the study, a total of 27 healthy participants underwent classical placebo conditioning, and then rated their pain experience associated with nociceptive-specific laser pulses delivered to the right hand dorsum. On each trial, different visual cues signaled the occurrence of a laser stimulus alone or of a laser stimulus accompanied by a sham analgesic treatment. During the conditioning period, cues signaling the sham treatment were followed by laser stimuli whose intensity was surreptitiously lowered. In the test period, either cue was followed by laser stimuli of the same intensity. The observation of facial expressions with different emotional content significantly enhanced the placebo analgesia. In particular, a significantly greater analgesic effect was observed when facial expressions with emotional content were presented concomitantly to the nociceptive stimulation. The authors reported that the enhancement of placebo analgesia during the observation of facial expressions was not correlated with personality traits such as empathy and behavioural activation/inhibition. The study is the first to quantify the effect of facial expressions on the magnitude of placebo analgesia.
Fuss I, Angst F, Lehmann S, Michel BA, Aeschlimann A. Prognostic factors for pain relief and functional improvement in chronic pain after inpatient rehabilitation. Clin. J .Pain. 30(4), 279–285 (2014).
In this prospective cohort study using standardized questionnaires on sociodemographic data, disease outcome, psychosocial factors, change in behavior, and outpatient therapies on discharge from inpatient rehabilitation and during the 5-month follow-up at home (observation period) the authors aimed to determine the factors associated with pain relief and improved physical functioning in chronic pain patients.
A total of 80.1% of the study’s participants were female, 90.0% had at least one comorbidity and 62.9% had chronic pain for ≥5 years. On average, pain intensity and depression worsened slightly during the observation period, but the other outcomes remained almost stable. Relief from anxiety and low baseline depression were the most important predictors for pain relief. Relief from anxiety and low baseline depression were most strongly associated with functional improvement.
The authors reported a strong association of change in pain severity and physical functioning with change in baseline level of affective health and coping during the first outpatient management period after inpatient rehabilitation. They therefore opined that it may be possible to improve the treatment of chronic pain by therapy of mood and coping.
Financial & competing interests disclosure
D Chamberlain is an employee of Future Science Group. The author has no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.
No writing assistance was utilized in the production of this manuscript.