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News from the field of neuropathic pain

Three recent articles digested for you by the Institute of neuropathic pain: May 2010

Postherpetic neuralgia

The German authors Mahn and Baron wrote an authorative review om postherpetic Neuralgia. ^[1].

Clinnicaly the authors point out that 1n 1 in 5 cases of herpes zoster, the manifestation can be found within the territoir of the trigeminal nerve. Postherpetic neuralgia is persisting pain in the zoster-affected area 6 months after healing of the zoster eruptions. The incidence epends on the patient's age: 50 - 75 % of patients in the seventh decade develop neuralgia after a zoster eruption. Three different pain types can be distinguished:

spontaneous, constant, burning pain,
intermittent sharp, lancinating pain and
pain in response to a normally non-painful stimulus (allodynia).

The pathogenesis is based on peripheral and central sensitisation as well as on spontaneous activity of damaged afferent nociceptive fibres as the consequence of changes in channels on the neuron's membrane.

In treating this pain the basic rule in the treatment of neuropathic pain syndromes should be followed: medication should be taken for at least 2 - 4 weeks before making a final evaluation.

One can choose from antidepressants, antiepileptics, opioid analgesics and topically acting agents.such as ccapsaicin and lidocaine.

Withdrawal symptoms after gabapentin discontinuation

Hellwig, Hammerquist and Termaat described withdrawal symptoms after gabapentin discontinuation. ^[2] They described a patient, were gabapentin was stopped after entry in a hospital: At the 3rd day the patient developed restlessness, disorientation, confusion, agitation, and anxiety. She was treated with benzodiazepines but had no improvement in symptoms. During days 4 and 5, the patient became increasingly confused, agitated, and anxious, with complaints of headache, light sensitivity, and increasing nervousness. On day 5, gabapentin was reinitiated, and the patient's confusion and agitation improved that evening. The next morning, the patient was calm, alert, and cooperative. Her symptoms resolved, and she was discharged on hospital day 7.

Clearly a lesson to taper out all patients on anti-epileptic medications...inlcuding these new drugs.

Venlafaxine or gabapentin in post OK pain?

Amr and Yousef published an important paper comparing the efficacy of the perioperative administration of Venlafaxine or gabapentin on acute and chronic postmastectomy pain. ^[3] One of the rare papers with a direct comparison between two analgesics. The study was carried out on 150 patients, randomized in a double-blinded manner to receive, extended release Venlafaxine 37.5 mg/d, gabapentin 300 mg/d, or placebo for 10 days starting the night before operation.

Venlafaxine 37.5 mg/d extended release or gabapentin 300 mg/d have equipotent effects (except on the first day in venlafaxine group) in reducing analgesic requirements, although gabapentin is more effective in reducing pain after movement. Venlafaxine significantly reduced the incidence of postmastectomy pain syndromes (chronic pain) 6 months in women having breast cancer surgery. Gabapentin had no effect on chronic pain except decreasing incidence of burning pain.

May 2010, Jan M. Keppel Hesselink, MD, PhD

Referenties

[1]: Mahn F, Baron R. | [Postherpetic neuralgia]. | Klin Monbl Augenheilkd. | 2010 May;227(5):379-83. Epub 2010 May 20.

[2]: Hellwig TR, Hammerquist R, Termaat J. | Withdrawal symptoms after gabapentin discontinuation. | Am J Health Syst Pharm. | 2010 Jun 1;67(11):910-2.

[3]: Amr YM, Yousef AA. | Evaluation of efficacy of the perioperative administration of Venlafaxine or gabapentin on acute and chronic postmastectomy pain. | Clin J Pain. | 2010 Jun;26(5):381-5.