The "velocity" of publications on IMC and headache seems to be decreasing, particularly on the use of IMC for the treatment of TACs. The science behind the understanding of the putative mechanisms of IMC's action on headache has moved forward, but the answer to why it works better than other nonsteroidal anti-inflammatory drugs has been elusive. There are case reports of other rare headache disorders that may be responsive to IMC. The dosages of IMC used as a tool for detecting IMC responsive disorders vary according to different centers of investigation. In many circumstances, headache disorders similar to "primary" IMC-responsive disorders are actually symptomatic disorders. Cluster headache as an IMC-resistant headache disorder may not be as absolute as once thought. Sometimes, IMC has been found to provoke headache; differentiating IMC-provoked headache from IMC-resistant headache can make headache diagnosis and management difficult. As for the "absolute" responsiveness of IMC, it is possible that using higher dosages leads to higher sensitivity, probably at the expense of decreased specificity. There are many reports about the occurrence of two or more IMC-responsive disorders (latu sensu) in the same patient, which may be coincidental.