Fig. 1

PTH clusters. Two PTH clusters were identified (a). Cluster 1 contained 140 (46.7%) patients and 160 (53.7%) patients assembled in Cluster 2 (a). One hundred and six (76%) Cluster 1 patients had persistent PTH while 133 (83%) of Cluster 2 patients had acute PTH. Compared to Cluster 2 patients, Cluster 1 PTH patients had higher prevalence of a history of migraine (MigHis), medication overuse (MO), pre-existing psychological history (PPH), new PTH-associated comorbidities (NewCom), history of repeated head injuries (PrevHI) compared to Cluster 2 PTH patients (a). The top 3 important predictors were a history of migraine, higher level of medication overuse and pre-existing psychological history (b). The bars in a show relative distribution of the different clinical variables - with the right bar in each cluster representing present clinical variable while the left bar is for absent variable. For example, the first row for history of migraine (MigHis) shows that Cluster 1 had relatively higher prevalence compared to Cluster 2. The seven bars in previous head injury (PrevHI) represent frequency of head injuries ranging from 0 (left) to 7 (right) under each cluster; there were more patients with more frequent head injuries in Cluster 1 compared to Cluster 2. Age distribution is shown ranging from 18 (left) to 90 (right) years. For sex, left bars represent males while right bars represent females