Proposal of changing subtype 8.1 "Headache induced by acute substance use or exposure" and subtype 8.3 "Headache as an adverse event attributed to chronic medication" of ICHD-II

Headaches as adverse reactions and symptom of intoxication, are included in subtype 8.1 of ICHD-II, even if, for example, headache induced by phosphodiesterase inhibitors has a completely different pathogenesis from headache induced by carbon monoxide or by cocaine. We propose a revision of subtypes 8.1 and 8.3, so that the classification could be used in clinical setting to diagnostic and therapeutic aims. In literature, adverse reactions are divided into two types: pharmacological (type A) and non-pharmacological ones (types B). Adverse reactions of type A are an extension of the main pharmacological action of the drug and are induced by an increase in pharmacological activities (A=augmented). They are frequent, foreseeable, dose-dependent, with high morbidity, but practically non-existent mortality, and can be already detected in the pre-clinical phase of the study of the drug. Non-pharmacological adverse reactions are not related to the main pharmacological action, they are an unusual and/or unexpected effect of the medication (B=bizarre), rare and unforeseeable, they have very low morbidity, but they can be mortal, and they often only appear after prolonged treatments. However, headaches as adverse reactions which are not induced by an increase in the main pharmacological activity of the drug (i.e., which cannot be classified as type A) do not belong to type B, since they can be frequent, but never rare or mortal, and they often also appear after prolonged treatments. This is the case of headaches induced by antimicrobials, antiviral agents, interferons, corticosteroids, and H2 receptor antagonists. These headaches are probably caused by factors such as benign intracranial hypertension, flu-like syndrome, or aseptic meningitis. We only define these adverse reactions as non-A-non-B in order to easily indicate them. We propose to classify the headaches of subtypes 8.1 and 8.3 into 4 subforms: 1. headaches induced by drugs which can also worsen a pre-existent headache; they are divided into two subgroups, depending on the pathogenesis of the headache as an adverse reaction (- type A; - type non-A-non-B); 2. food additive-induced headaches; 3. acute or chronic intoxication-induced headaches; 4. exogenous hormone-induced headache. We propose that food-induced headaches should be moved to the appendix, to indicate that further evidence is needed to prove their real existence. In particular, we need to increase the number of clinical case histories with objective instead of anecdotal data, in order to decide whether they are a clinical reality or rare to the point of being unique cases.