Very few patients with S-L TM could be classified with a single diagnosis in the ICHD-2 classification. In fact, ICHD-2 CM was so rare that it would be virtually impossible to conduct clinical trials of this check details entity diagnosed using ICHD-2 criteria. The authors proposed that clinical trials of this entity should therefore be conducted using the S-L criteria. In the same database, alternative definitions for CM were explored. The percentages of patients who met modified criteria for CM were 47.4% when 15 or more days of migraine or probable migraine were required, 90% when migraine or probable migraine on ≥50% of the headache days was required, and 96.7% when >8 days of migraine or probable

migraine per month were required. Among those overusing medication, the percentages of patients meeting CM criteria were 37.1% when 15 or more days of migraine or probable migraine were required, 83.3% when migraine or probable migraine on ≥50% of

the headache days was required, and 90.0% when >8 days 17-AAG in vitro of migraine or probable migraine per month were required. The same group conducted a similar study in adolescents with similar results.[41] Of the 69 patients with S-L TM without medication overuse, most (71%) could be classified as having ICHD-2 CM. However, of the patients with TM with medication overuse (n = 48), just 39.6% met criteria for probable CM. Most patients (94.2% of those not overusing medication and 91.6% of those overusing medication) had migraine or probable migraine on at least 50% of the headache days. The data demonstrate that the ICHD-2 criteria for CM are too restrictive for clinical practice. In addition, the criteria are inappropriate for clinical trials because they exclude the patients who would be the intended targets of treatment. Accordingly, a revision in 2006, ICHD-2 (ICHD-2R),[42]

requiring that patients have 15 or more headaches per month with ≥8 days of headaches that meet criteria for migraine without aura or that respond to migraine-specific therapy was proposed (Table 2).[42] The ICHD-2R criteria were field tested in a sample of patients from NECH diary study.[43] The ICHD-2R criteria were also evaluated against 3 proposals. In proposal 1, CM/CM+ would require at least 15 days of migraine or probable migraine per month. Proposal 2 required click here ≥15 days of headache per month, with at least 50% of these days being migraine or probable migraine. This definition, which largely overlaps the ICHD-2R criteria, had been recommended by Silberstein, Bigal, and Lipton for use in clinical trials.[15] Proposal 3 required ≥15 days of headache and at least 8 days of migraine or probable migraine per month. The results show that of the 158 patients with TM, just 5.6% met ICHD-2 criteria for CM, whereas 92.4% met ICHD-2R criteria for CM. The ICHD-2R criterion performed better than proposal 1 (47.