Trigeminal neuralgia (TN) is a rare neuropathic facial pain disorder. Two forms of TN, classical TN (CTN) and atypical TN (ATN), are reported and probably have different aetiologies. The aim of the present study was to evaluate the functional integrity of the diffuse noxious inhibitory controls (DNIC) in (1) a group of patients with classical trigeminal neuralgia (CTN), (2) a group of patients with atypical trigeminal neuralgia (ATN), and (3) a group of healthy controls in order to determine if a descending pain modulation deficit could participate in the pathophysiology of TN pain. DNIC responses of 14 CTN patients, 14 ATN patients and 14 healthy controls were obtained by comparing thermode-induced facial heat pain scores before and after activating DNIC. DNIC was triggered using a standard counter–irritation paradigm (i.e., immersion of the arm in painfully cold water). General sensitivity to pain was also evaluated by measuring mechanical pain thresholds over 18 points located outside the trigeminal territory. Healthy participants and CTN patients showed a 21% and 16% reduction in thermode-induced pain following the immersion, respectively (all p-values <.01), whereas ATN patients experienced no change (p = .57). ATN patients also had more tender points (mechanical pain thresholds <4.0 kg) than CTN and healthy controls (all p-values <.05). Taken together, these results suggest that the underlying physiopathology differs between CTN and ATN and that a deficit in descending inhibition may further contribute to the pain experienced by patients with ATN.
aUniversité de Sherbrooke, Faculté de médecine, Sherbrooke, Quebec, Canada J1H 5N4
bMoncton Hospital, Moncton, New-Brunswick, Canada E1C 6Z8
*Corresponding author. Address: Université de Sherbrooke, Faculté de médecine, neurochirurgie, Équipe de recherche sur la douleur, 3001, 12e avenue nord Sherbrooke, Québec, Canada J1H 5N4. Tel.: +1 819 346 1110x15889; fax: +1 819 564 5424.
Received March 6, 2009
Received in revised form September 4, 2009
Accepted September 9, 2009.