[The effectiveness and safety of botulinum toxin in the treatment of chronic primary headaches].

INTRODUCTION: Primary headaches (PH), which are highly prevalent pathologies, are linked to high morbidity and disability rates and high costs for the health care system. Due to the partial effectiveness of prophylactic treatments, especially in chronic headaches, or the existence of contraindications that make them unsuitable for prescription, the use of botulinum toxin (BTX) arises as a promising preventive therapy.

AIMS: The purpose of this study was to determine the usefulness and the mechanism of action of BTX in PH through a review of the literature.

DEVELOPMENT: Recent results of BTX use in PH are contradictory and, although controlled studies with placebos are scarce, it has been suggested that it could have a grade II-III evidence level of effectiveness and safety, with greater benefits in refractory chronic migraine and chronic tension-type headache, together with the absence of analgesic abuse and psychiatric illness. The probable mechanism of action in PH is through a peripheral antinociceptive effect related to a decreased release of neuropeptides and to the transmission of impulses with indirect inhibition of nociceptive centres in the brain stem, which is an effect that is apparently intensified with repeated applications. A correlation has been claimed between the use of BTX and a reduction in the intensity, severity, number of headaches per month, diminished use of analgesics per month and lowered total management costs. Side effects of the treatment are infrequent (< 1%) and transient.

CONCLUSIONS: Despite findings that have proved BTX to be effective and safe as prophylactic therapy in PH, it is still not considered to be the first choice preventive treatment. Further studies are needed to establish sites, doses and application schemas (fixed vs. mobile), as well as a subtype of patients who can benefit from its use.