Our study evaluated the prevalence of psychiatric comorbidity and specific personality traits in CDH patients. Headache and drug overuse were classified using both the original  and the revised International Classification of Headache Disorders-II (ICHD-II)  criteria to clearly differentiate the type of prevalent headache (migraine vs tension-type headache) and the presence of drug overuse.
In our sample drug overuse is significantly increased in pCM + pMOH patients with respect to pCTTH + pMOH patients, probably due to the pain severity of their attacks.
Of the 94 subjects included in the sample, 46.8% showed psychiatric comorbidity. The disorders most frequently diagnosed were mood and anxiety disorders (43.6%). These data are in line with some previous literature [26, 37–39], indicating that the most common psychiatric conditions related to migraine were depression, bipolar disorders, anxiety  and somatoform disorders. However, the relationship between CDH and psychiatric disorders is still matter of debate in the literature, this being also due to the different headache diagnostic criteria and the different methods adopted in most of the studies to assess psychiatric disorders [12–16]. Verri and colleagues  found an association between CDH and at least one psychiatric disorder in 90% of their patients. Juang and colleagues  found that the frequency of any type of anxiety disorder was significantly higher in patients with CM than in those with CTTH. This was not confirmed in our sample in which no differences were found in psychiatric comorbidity between the migraine and the tension-type headache groups, and between patients with and without drug overuse. These findings are in agreement with the results obtained by Atasoy and colleagues  who analyzed psychiatric comorbidity in 89 MOH patients and did not find any difference in MOH patients with pre-existing episodic tension-type headache (ETTH) with respect to those with pre-existing MWOA.
Psychiatric comorbidity has often been clinically discussed rather than systematically studied. The use of M.I.N.I., a structured clinical psychiatric interview , helped us to establish a diagnosis on reliable and valid diagnostic criteria. Although M.I.N.I. is considered a somewhat overinclusive instrument in ‘making diagnosis’ , it indicated the presence of depression in our sample, while HAM-D results revealed that the mood disorder was milder than expected. Moreover, after clinical interviews, psychiatrists reported that psychiatric disorders in MOH appear in subthreshold forms rather than as full-blown disorders. Even if the percentage of patients assuming prophylactic therapies with antidepressant or mood stabilizer drugs was similar in both groups, with and without psychiatric comorbidity, we can not exclude a role of these drugs in the final results.
Previous MMPI-2 results stressed the presence of the “neurotic MMPI-2 profile” in headache patients, a profile characterized by a high level of depression, hypochondria and hysteria [27, 30, 31]. We found that in our sample, the neurotic triad was detected only in patients with psychiatric comorbidity, while patients without psychiatric comorbidity displayed a high score only in the Hypochondriasis subscale, indicating high concern for their health status. The presence of the “neurotic MMPI-2 profile” in chronic headache has already been the focus of previous studies [27, 28] arguing that these personality traits appeared to be a reaction to chronic pain rather than a specific feature of headache patients . Our results suggest for the first time that the “neurotic MMPI-2 profile” was not associated to headache per se, but was a dominant feature in headache patients who showed comorbidity with psychiatric disorders. However the cross-sectional design of the study does not permit to reveal any casual relationship.
The two groups also differentiated for scores in Addiction Potential Scale: patients with psychiatric comorbidity had higher scores than patients without, even if the scores fell in the normal range. Furthermore, the presence of medication overuse was not a discriminating factor. These data support Galli et al.’s  hypothesis that medication overuse in CDH patients might not be related to dependence, but rather might be a consequence of chronic pain. From this perspective, medication overuse could be seen as the only way patients know to cope with their pain and maintain a normal lifestyle. However, this hypothesis conflicts with other studies on dependence in patients with MOH . Specific instruments are needed to assess dependence behavior in MOH patients as it seems to have different theoretical constructs from classic dependence behavior .
A high score in MMPI-2 Health Concern subscale was found in all CDH patients suggesting concern for their general health condition, and not only for their headache. This result is concordant with the elevated score also found in the Hypochondria clinical scale.
We acknowledge the limitations of the present study, the principal one being that it was performed in a tertiary care headache clinic so that the investigated sample may not represent the whole spectrum of CDH patients in the general population. Another limitation was that MMPI-2 was properly completed only by 83 of the 94 subjects included. Another major problem was the diagnostic distinction of CDH and drug overuse that remains controversial and could introduce a selection bias. We tried however to overcome this limitation, which is intrinsic to all studies investigating headache chronification, by applying the IHS revised criteria for headache diagnosis.