Objectives-To study the clinical and pathophysiological features of central pain due to damage to the CNS. Methods-156 patients (mostly with ischaemic strokes, some with infarct after subarachnoid haemorrhage and other cerebral conditions; one with bulbar and others with spinal pathology) with central pain have been investigated clinically and varying numbers instrumentally with respect to quantitative somatosensory perception thresholds and autonomic function. Results-Pain onset was immediate in a minority; and from a week or two up to six years in > 60%. For those with supraspinal ischaemic lesions, the median age of onset was 59; dominant and nondominant sides were equally affected. Two thirds of the patients had allodynia, including a previously undescribed movement allodynia apparently triggered from group I afferents. Most patients exhibited autonomic instability in that their pain was increased by physical and emotional stress and alleviated by relaxation; cutaneous blood flow and sweating may also be affected. Pain occurred within a larger area of differential sensory deficit. The critical deficit seems to be for thermal and pinprick sensations, which were more pronounced in areas of greatest than in areas of least pain; whereas low threshold mechanoceptive functions, if affected, did not vary between areas of greatest and least pain. Skinfold pinch (tissue damage) pain thresholds were only slightly affected in supraspinal cases, but greatly increased in patients with spinal lesions; thermal (heat) pain did not show this dissociation. Conclusion-The pathogenetic hypothesis which seems best to fit the findings is that there is up regulation or down regulation of receptors for transmitters, possibly mainly noradrenergic, over time.

Seventy-two patients older than 60 years of age who received a diagnosis of herpes zoster (HZ) were entered into a randomized, double-blind, placebo-controlled trial of daily amitriptyline 25 mg. Treatment with either amitriptyline or placebo continued for 90 days after diagnosis. Pain prevalence at 6 months was the primary outcome. Results showed that early treatment with low-dose amitriptyline reduced pain prevalence by more than one-half (p < 0.05; odds ratio, 2.9:1) This finding makes a strong case for the pre-emptive administration of amitriptyline, in combination with an antiviral drug, to elderly patients with acute herpes zoster.

One-thousand-and-seventy-one randomly chosen elderly persons (537 women, 534 men; median age 80) were recruited from the Institute of Human Aging (Dept of Psychiatry, University of Liverpool). Almost a quarter (23.8%; equal numbers of both sexes) had had shingles (HZ), at a median age of 60 (for both sexes); 39 subjects (3.6% of all respondents, 15% of those who had had shingles), two thirds of whom were female, developed post-herpetic neuralgia (PHN), defined as pain persisting for more than 3 months; they acquired HZ at a median age of 70. In 22 of them, pain had resolved by the time they were questioned, but in 17 it was ongoing (from less than 12 to 504 months). Two new independent risk factors for PHN were identified: (1) female gender; and (2) living alone at the time of HZ acquisition (p = 0.009). In addition to confirming the well-known factor of: (3) age at shingles acquisition (up to the early 90s); and (4) scarring, presumed to be a consequence of rash severity, was significantly commoner in subjects whose HZ was followed by PHN.Extrapolating the prevalence figures to the whole UK population, of whom 9.28 million were over 64 in 1992, it can be conservatively estimated that at any one time, some 200 000 people in the UK have PHN. Copyright 1999 European Federation of Chapters of the International Association for the Study of Pain.

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