Patients and Methods: Genotype polymorphism analysis was carried out in 26 patients with chronic tension type facial pain unresponsive to or recurring after treatment with amitriptyline. Findings were compared to 33 asymptomatic age-and gender-matched controls. Blood serotonin levels in these two groups were also determined. 

Results: Consistent with previous studies, patients with chronic pain had significantly lower blood serotonin compared to controls. In all genotypes, blood serotonin was low compared to controls and this was significant in patients homozygous for the L allele. 

Conclusion: In this small pilot study, patients with the LL genotype seemed to have the best clinical outcome after three-year follow-up.