Here, we are the first to report three cases of scalp temperature changes in symptomatic areas affected by nummular headache, which may provide an enriched understanding of the variation in clinical manifestations of nummular headache. Scalp temperature changes are a form of paraesthesia, which may have clinical implications for its peripheral pathogenesis. The exact pathogenesis of nummular headache has not been clearly defined. Studies have advanced two main hypotheses: a peripheral mechanism and a central mechanism. Pareja and his colleagues have classified nummular headache as a localized neuralgia stemming from epicranial tissues – specifically, neuralgia affecting a terminal branch of one of the cutaneous nerves of the scalp [
11]. The skin and hair changes in the symptomatic area also reflect a peripheral nerve lesion or, alternatively, an autoimmune process [
12,
13]. In an extensive case series, Cuadrado and his colleagues reported that nummular headache was associated with a local increase in pain sensitivity to mechanical stimulation (reduced pressure pain thresholds [PPTs]) confined to the symptomatic area [
14]. Although the pain is asserted to originate from epicranial tissues including the skull, scalp, vessels, and nerves [
15‐
17], some nummular headaches have been described as “symptomatic nummular headaches”, which implies that they might be secondary to underlying structural lesions or other causes, such as subtentorial meningioma [
10], pituitary lesion [
18], or arachnoid cysts [
19]. These observations represent the secondary form of nummular headache. Some researchers have also reported that nummular headache may arise from intracranial lesions or stress, both of which need to be ruled out when this type of headache appears [
19]. Aside from these pathogenetic hypotheses, some researchers have suggested that nummular headache is caused by psychiatric disturbances [
15]. However, other researchers have excluded the possibility of psychological factors as a cause of nummular headache disorder, and it is important to note that depression and anxiety are not symptoms of nummular headache disorder. Patients suffering from nummular headache disorder showed mood states similar to those of a healthier person [
20]. We have discussed the pathogenesis of nummular headache, and we believe the observed changes in scalp temperature might be a clue in this mystery. However, we could not absolutely exclude the central hypothesis or the possibility of a complex pathogenesis involving both peripheral and central mechanisms. Further studies are still needed to help unveil the mystery.
In the initial report by Pareja in 2002, nummular headache was established to be a primary disease with clear-cut clinical features including a single, circumscribed location and mild to moderate pain. The three cases that we report in this paper involved paraesthesia, with the affected areas of the scalp being colder or warmer than the normal areas. This finding might support a peripheral mechanism of nummular headache. However, we could not definitively exclude the central hypothesis [
21], and future studies with larger samples and follow-up designs may reveal a central mechanism as the cause of nummular headache. The ultimate judgement must be made by the appropriate healthcare professional(s) responsible for decisions regarding specific clinical procedures and treatment plans.