The pathogenesis of chronic pain syndromes

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Abstract
In chronic pain syndromes in which no organic pathology or pathophysiological mechanism can be found to account for the pain, i.e. the idiopathic pain syndromes, there is a high frequency of sadness, inner tension and inhibition-retardation. The clinical similarities between the idiopathic pain syndromes and the depressive syndromes have led to the hypothesis that the two syndromes have a common pathogenetic mechanism, that the idiopathic pain syndrome is a masked depression, a special syndrome in a spectrum of depressive diseases or simply a variant of the depressive disorders. In a series of studies, patients with idiopathic pain syndromes have been found to have a high frequency of subjects with affective disorders among their first degree relatives, many have had earlier depressive episodes before the start of the pain syndrome and in about 1/4 of the patients there is a clearcut major affective episode concurrently with the idiopathic pain syndrome. Furthermore, the REM latency in sleep EEG is shortened, there is hypercortisolaemia and a high frequency of pathological dexamethasone suppression tests, low concentrations of the serotonin metabolite 5-HIAA in the C.S.F., low activity of the MAO enzyme in platelets, low 3H-imipramine receptor binding, low concentrations of substance P in the C.S.F., low concentrations of melatonin in serum and urine, high concentrations of endorphins. Fraction 1 in the C.S.F. and low concentrations of dynorphin in the C.S.F. Thus many of the biochemical disturbances usually found in patients with affective disorders are also found in patients with idiopathic pain syndromes and the data today seem to favour the hypothesis that the two syndromes at least have a common pathogenetic mechanism. Among the possible pathogenetic mechanisms found, there is the strongest support for disturbances in the serotonergic systems and thus treatment with serotonin reuptake inhibitors is of great interest. □ Biological markers, Chronic pain, Idiopathic pain, Pathogenesis, Serotonergic disturbances.