Effect of exposure to sauna heat on neuropathic and rheumatoid pain.

Exposure to sauna heat during sauna bathing raises the skin temperature of the bather near the hot pain perception threshold and enhances sympathetic activity. Self-reports provided by regular bathers of changes in intensity of their ongoing pain might, therefore, add novel information on the effect of intense heat on various pain conditions. We interviewed consecutive patients attending our pain clinic over a period of 1 year about their pain-related responses to sauna bathing and controlled the results by quantitated somatosensory tests. There were 61 patients with chronic neuropathic pain of peripheral origin, 13 patients with central pain and 59 patients with rheumatoid pain. Allodynia and hyperalgesia to heat were relatively infrequent in all groups (10%, 15% and 8%, respectively). Three out of 17 patients with postinjury nerve pain reported similar exacerbation. By contrast, mechanical allodynia was present in 48% of patients with peripheral neuropathic pain and in 54% of patients with central pain. The results speak against an important role for C-afferent or sympathetic postganglionic fibres in most subclasses of neuropathic pain. Animal models of neuropathic pain should be critically viewed against this finding.