Alteration of the antinociceptive systems in chronic daily headaches

Introduction. Chronic daily headache (CDH) is a chronic painful clinical condition that is frequently found in neurological practice. Diagnosis is clinical and the therapeutic approach is complex. Its mechanism of production is still not altogether clear but a genetic component is acknowledged as a predisposing factor. Numerous areas are involved in the generation of primary headaches, including the periaqueductal grey matter (PAGM), which plays a role as a neuromodulator both in headaches and in other chronic painful conditions. Aims. In order to evaluate possible biochemical changes in patients with CDH, magnetic resonance imaging was used to study the spectra produced in the PAGM. Subjects and methods. The spectra in the PAGM were studied in 17 patients with CDH. These were compared with the average spectra in 17 healthy subjects by means of differential spectroscopy. Results. Subjects with CDH show a reduction of over 70% in the level of the metabolite N-acetyl-aspartyl-glutamate (NAAG) in the PAGM. NAAG is a peptide involved in antinociceptive activity. Conclusions. The reduction of NAAG in the PAGM suggests altered neuromodulation of the antinociceptive systems in subjects with CDH. Whether CDH is the cause or the consequence has still to be determined.