Medication overuse headache (MOH) is a disabling disorder occurring when a subject with a primary headache disorder begins to suffer from a chronic headache, presumably due to a too frequent use of drugs usually assumed to extinguish pain. The term “medication-overuse headache” was first used in the second edition of the ICHD[1] although a “drug-induced headache” was previously described in its first edition. In the last edition of International Classification of Headache Disorder,[2] MOH is listed as a secondary headache, in the section focused on “Headache attributed to a substance or its withdrawal”.
Although pathophysiologic mechanisms of MOH are still largely unclear, a genetic predisposition likely plays an important role.[3, 4] Another potentially significant pathogenetic factor taken into consideration is the interaction between drugs used and neurotransmitters[5] and/or hormonal systems.[6] Other factors investigated over time include the presence of abnormal neuronal excitability[7] and changes in grey matter volumes[8] and cerebral metabolism.[9–11]
The overall prevalence of MOH in the general population is 0.5–2.6%, although it varies between different studies, probably as a consequence of different diagnostic criteria published over time and different methods used to collect epidemiological data.[11, 12] Very few epidemiological studies are available in pediatric population. Data from Norway and Taiwan report prevalence rate of 0.2% and 0.3% respectively.[13, 14] Data from pediatric populations with chronic primary headache disorders report a medication overuse in 10–60% of cases.[15] Both in adults and children, MOH appears to be more common among females than males.[16, 17]
Clinical features are usually the same of preexisting primary headache disorder.[11] In pediatric patients, it is more commonly associated with chronic migraine (CM).[18] Non-steroid anti-inflammatory drugs (NSAIDs) are the class of drugs more often overused, followed by paracetamol and triptans.[16] Historically, the treatment of MOH includes two main strategies: a detoxification program with discontinuation of drugs overused, and initiation of pharmacological and nonpharmacological preventive therapy.[11]
In the last two decades, diagnostic criteria for MOH were gradually changed. Initially, MOH could be diagnosed only if the headache resolved or reverted to the previous pattern within 2 months after withdrawal of the overused medication.[19] In the revision of diagnostic criteria published in 2006,[20] the Headache Classification Committee proposed to remove the criterion concerning the effect of drug suspension on headache course, and this modification was kept in the last published version of ICHD-3 (Table 1).[2]
Table 1
Diagnostic criteria for MOH by ICHD-2 (2004)[1] and by ICHD-3 (2018)[2].
ICHD-2 | ICHD-3 |
A.Headache present on ≥ 15 days/month fulfilling criteria C and D B.Regular overuse2 for ≥ 3 months of one or more drugs that can be taken for acute and/or symptomatic treatment of headache C.Headache has developed or markedly worsened during medication overuse D.Headache resolves or reverts to its previous pattern within 2 months after discontinuation of overused medication | A. Headache occurring on ≥15 days/month in a patient with a pre-existing headache disorder B. Regular overuse for > 3 months of one or more drugs that can be taken for acute and/or symptomatic treatment of headache C. Not better accounted for by another ICHD-3 diagnosis. |
Therefore, MOH can be presently diagnosed in a subject with a history of a preexisting primary headache, presenting with headache occurring 15 days per month in association with a regular medication use exceeding specific thresholds.
A direct consequence of new criteria could be an increase of definite diagnosis, since MOH can now be diagnosed even in the absence of improvement after drugs withdrawal. However, diagnostic criteria and even the existence of this specific nosographic entity are not universally accepted. For instance, some authors wondered whether medication overuse is the real cause of headache in all subjects fulfilling diagnostic criteria for MOH.[15, 19, 21] Indeed, in some individuals medication overuse can increase headache frequency, and discontinuing the medications can have a benefit, but this is not the case in all individuals overusing medications. In some case, increasing headache frequency represents a worsening of the primary headache disorder, and increased use of acute medications is its consequence.[15]
Aim of our study was to compare the rate of patients diagnosed with MOH according to the old ICHD-2 and new ICHD-3 criteria, in order to verify the degree of concordance and understand if the new classification really led to different diagnostic rates. Secondary aim was to verify if drug withdrawal is really associated with pain relief, and therefore to investigate in a large sample of pediatric patients whether MOH is a true entity.