Comorbidity refers to the greater than coincidental association of separate conditions in the same individuals. Comorbidity may be an artifact of diagnostic uncertainty when symptom profiles overlap or when diagnosis is not based on objective markers. Comorbidity may arise due to unidirectional causality, such as migraine resulting in blood pressure changes due to headache-specific treatment. Finally, conditions may be comorbid because of shared genetic or other factors that increase the risk of both conditions. (Scher, 2005)
Migraine comorbid with depression is common and is often encountered in clinical practice. Numerous literature have showed that the comorbidity may have a common complicated pathogenic mechanism involving biopsychosocial characteristics, including abnormal brain development and shared genetic basis, as well as neurotransmitters, sex hormones and stress. In addition, some studies have identified the multiple, bidirectional relationship between migraine and depressive disorder. (Zhang, 2019)
Burch RC. Migraine: Epidemiology, Burden, and Comorbidity. Neurologic clinics. 2019;37(4):631-649. doi:10.1016/j.ncl.2019.06.001
Zhang Q, Shao A, Jiang Z, Tsai H, Liu W. The exploration of mechanisms of comorbidity between migraine and depression. J Cell Mol Med. 2019 Jul;23(7):4505-4513. doi: 10.1111/jcmm.14390. Epub 2019 May 20. PMID: 31106971; PMCID: PMC6584585.
Scher AI, Bigal ME, Lipton RB. Comorbidity of migraine. Curr Opin Neurol. 2005 Jun;18(3):305-10. doi: 10.1097/01.wco.0000169750.52406.a2. PMID: 15891417.