The pathogenesis of tension-type headache (TTH) is still not yet completely understood. Previous studies have revealed an increased tenderness to muscle palpitation in patients with chronic tension-type headache (CTTH). In addition, lower pressure pain thresholds (PPT) were observed in cephalic and extracephalic muscles when compared to healthy subjects. This increased tenderness to palpitation and the decreased PPT levels may be due to increased excitability of peripheral nociceptors, increased sensitivity in the central nervous system, or a reduction in inhibitory mechanisms. Mechanical hypersensitivity of muscle tissues is generally regarded as a common clinical manifestation of central sensitization in CTTH.

The application of non-noxious mechanical stimuli to nonsensitized peripheral nerves is painless. Therefore, pain elicited by manual palpation of a peripheral nerve during a physical examination is usually considered to reflect peripheral sensitization of the nerve or central sensitization.

The present study aimed to evaluate (1) differences in the perception of pain following palpation of the supra-orbital nerve (V1) between patients with CTTH and healthy subjects; (2) differences in PPT levels for the V1 nerve between patients with CTTH and controls; and (3) whether local pain to palpation or pressure pain sensitivity of the V1 nerve in the CTTH group was related to the intensity or the temporal profile of the headaches.

Twenty patients with CTTH and 20 healthy controls participated in this study. An 11-point numerical pain rating scale was used to assess headache intensity. A headache diary was used to calculate the following variables: (1) headache intensity; (2) headache frequency; and (3) headache duration. A mechanical pressure algometer was used to measure pressure pain threshold. Pressure was applied in random order over the left and right supra-orbital nerves at the supra-orbital notch. Palpation was performed by applying pressure over the supra-orbital notch during small rotational movements of the assessor’s fingers for 4 to 5 seconds. These maneuvers were conducted on both the patients and controls.

Patients with CTTH showed lower PPT levels and increased tenderness following palpation of the supra-orbital nerve compared to healthy controls, which indicate nerve mechanical hypersensitivity. Further, nerve mechano-sensitivity was significantly related to headache clinical parameters: the greater the headache intensity, duration, or frequency, the lower the PPT level or the greater the local pain to palpation. Mechanical nerve hypersensitivity suggests the existence of sensitization of nerve tissues, a possible perpetuating factor for sensitization of central pathways.