Indications for peripheral and central sensitization in patients with chronic scalp pain (trichodynia).

Objectives: The underlying mechanism of trichodynia (scalp/hair pain, is unknown). The aim of this study was to characterize chronic trichodynia and to conduct, for the first time, sensory testing in patients with trichodynia to learn about possible underlying mechanisms.

Methods: Participants were 16 trichodynia patients and 19 healthy controls. Participants underwent testing of touch and pressure-pain threshold as well as allodynia in painful and pain-free scalp sites and in the hands (intact remote region). A trichogram (hair test) was conducted on painful and pain-free scalp sites to evaluate hair cycle abnormalities. The chronic pain was characterized as well.

Results: Painful sites were characterized by decreased thresholds for light touch (P<0.01) and pressure pain (P<0.01) and high rates of static allodynia (94%) compared with adjacent pain-free sites and controls. A significant negative correlation was found between chronic pain intensity and scalp thresholds. Spontaneous and evoked pain existed only in scalp sites with hair cycle abnormalities. In addition, pressure-pain threshold in the hands was significantly lower in trichodynia patients compared with controls.

Discussion: The cranial hyperalgesia and allodynia, the generalized hyperalgesia, and the correlation between hyperalgesia and chronic pain suggest that trichodynia is related with both peripheral and central sensitization, respectively. The coexistence of hair cycle abnormalities and chronic pain might suggest a common denominator for both phenomena, possibly mediated by proinflammatory agents. Clinical implications are discussed.