Comments on Allena et al.: From drug-induced headache to medication overuse headache. A short epidemiological review, with a focus on Latin American countries

The selection criteria of the literature included in this review remain unclear. What were the criteria for “scientific validity”, “historical value”, “importance”, and “relevance”?

What supports the authors’ statement that “prevalence (of MOH) is increasing worldwide”? The quoted review by Diener and Limmroth [2] includes the statement “there is increasing evidence that the overuse of analgesics and subsequent MOH is not only prevalent in Europe and North America but is a growing problem in Asian countries—in China and Taiwan the prevalence is the same as in Europe”. The fact that data on MOH prevalence are reported from a growing number of countries cannot justify the claim of an “increasing prevalence”. The second review quoted by the authors—by Limmroth & Katsarava [3]—does not provide any corresponding evidence.

The “discussion of the relevant epidemiological data available on MOH, focusing on the information regarding this condition in Latin American (LA) countries” announced by the authors plainly should have been omitted, since there seem to be hardly any data at all.

Results from clinical case series (from specialized headache clinics) cannot be generalized due to the immanent selection bias, not even the extent of which can be assessed.

The authors quote the study by Meskunas et al. [4] which showed that in one US headache clinic the relative frequency (correctly not called prevalence by Meskunas et al.) of (probable) MOH remained stable (with a tendency to decrease) over 15 years when the number of tablets/day is considered, but the medications used have changed substantially. Moreover, they highlight MOH development with overuse of various triptans. Reports of occurrence of MOH exist for practically all analgesics and migraine medications—independent of their composition. Independent of whether MOH frequency could also correlate with the frequency of use of the active substance among the population, one explanation would be that MOH development is primarily related not so much to the use of certain substances in migraine and headache medications, but more to the frequency and dosage in a vulnerable subpopulation of patients with migraine and tension-type headache. This very obvious explanation has not even been considered by the authors.

Epidemiological studies do not unambiguously show whether frequent medication intake is the cause or consequence of chronic headache. Authors of various publications point this out explicitly. Unfortunately, this important information is missing in the review by Allena and co-authors.

The statement that ergotamine has been taken off the market in Germany is not correct. Tablets containing 2 mg ergotamine (Ergo-Kranit^®) are still available in Germany.

The reference of a study by Hering-Hanit and Gadoth [5] on the topic of MOH in children and adolescents in connection with their intake of caffeine is misleading, just as the statement that this indicates some early overuse. In their study, Hering-Hanit and Gadoth investigated the excessive caffeine consumption in the form of cola drinks, which can hardly be considered medications. Therefore, this paper cannot make a contribution to the evaluation of headache with medication overuse.