I was thinking about the chicken and egg conundrum, and how it relates to the discussion of whether illness comes before depression or vice versa, and I wondered if possibly inflammation comes first. Medical science tells us that inflammation is the root of most, perhaps all disease. To add to this idea, I reviewed Filakovic, Bijan, and Petek (2008), which found similar elevated levels of pro inflammatory cytokines in depression and psoriasis. These authors believed the basis of both disorders was shared inflammatory pathways mediated by the immune system.
Similarly, Potter and Steffans (2007) found depression was commonly diagnosed in individuals with mild cognitive impairment, which may lead to Alzheimer's Disease (AD). Maes et al., (2010) found depression was an antecedent to AD. The similarity is in the Maes et al. explanation that depression and neurodegenerative diseases, such as AD are the result of inflammation that is basically part of the same biological process, along the same inflammatory pathways. Maes et al. believed the degeneration of inflammatory pathways created a cycle in which neuroinflammation provoked neurodegeneration and created a process by which depression exacerbated the comorbidity, and vice versa.
This idea of disease-sharing pathways was fascinating to me. I wonder if comorbidities are not independent occurrences, but rather are two symptoms of the same process, it seems we will have to rethink the idea of comorbidities, such as anxiety and depression (Hirschfeld, 2001). Rather than treating two diseases or comorbidities, perhaps they will be treated as one degenerative process.
Filakovic, P., Bijan, D., & Petek, A. (2008). Depression in dermatology: An integrative perspective. Psychiatria Danubina, 20(3), 419-425.
Hirschfeld, R. (2001). The comorbidity of major depression and anxiety disorders: recognition and management in primary care. Primary Care Companion To The Journal Of Clinical Psychiatry, 3(6), 244-254.
Maes, M. (2010). An intriguing and hitherto unexplained co-occurrence: Depression and chronic fatigue syndrome are manifestations of shared inflammatory, oxidative and nitrosative (IO&NS) pathways. Progress in Neuro-Psychopharmacology and Biological Psychiatry. doi: 10.1016/j.pnpbp.2010.06.023
Potter, G. G., & Steffens, D. C. (2007). Contribution of Depression to Cognitive Impairment and Dementia in Older Adults. The Neurologist, 13(3), 105-117. doi: 10.1097/01.nrl.0000252947.15389.a9