An intriguing and hitherto unexplained co-occurrence: Depression and chronic fatigue syndrome are manifestations of shared inflammatory, oxidative and nitrosative (IO&NS) pathways.
There is a significant 'comorbidity' between depression and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). Depressive symptoms frequently occur during the course of ME/CFS. Fatigue and somatic symptoms (F&S), like pain, muscle tension, and a flu-like malaise, are key components of depression. At the same time, depression and ME/CFS show major clinical differences, which allow to discriminate them with a 100% accuracy. This paper aims to review the shared pathways that underpin both disorders and the pathways that discriminate them. Numerous studies have shown that depression and ME/CFS are characterized by shared aberrations in inflammatory, oxidative and nitrosative (IO&NS) pathways, like systemic inflammation and its long-term sequels, including O&NS-induced damage to fatty acids, proteins and DNA; dysfunctional mitochondria; lowered antioxidant levels, like zinc and coenzyme Q10; autoimmune responses to neoepitopes formed by O&NS; lowered omega-3 polyunsaturated fatty acid levels; and increased translocation of gram-negative bacteria. Some IO&NS-related pathways, like the induction of indoleamine 2-3-dioxygenase, neurodegeneration and decreased neurogenesis, are more specific to depression, whereas other pathways, like the 2'-5' oligoadenylate synthetase/RNase L pathway, are specific to ME/CFS. Most current animal models of depression, e.g. those induced by cytokines, are not reminiscent of human depression but reflect a mixture of depressive and F&S symptoms. The latter symptoms, sometimes called sickness behavior, differ from depression and ME/CFS because the former is a (sub)acute response to infection-induced pro-inflammatory cytokines that aims to enhance recovery, whereas the latter are characterized by long-term sequels in multiple IO&NS pathways. Depression and ME/CFS are not 'comorbid' disorders, but should be regarded as 'co-associated disorders' that are clinical manifestations of shared pathways.
Maes
Michael
M
Maes Clinics @ TRIA, 998 Rimklongsamsen Road, Bangkok 10310, Thailand. dr.michaelmaes@hotmail.com
D000818:Animals; D015897:Comorbidity; D003863:Depression / Q000453:epidemiology* / Q000276:immunology / Q000503:physiopathology; D015673:Fatigue Syndrome, Chronic / Q000453:epidemiology* / Q000276:immunology / Q000503:physiopathology; D006801:Humans; D007249:Inflammation / Q000150:complications / Q000276:immunology / Q000378:metabolism*; D015538:Nitrosation / Q000502:physiology*; D018384:Oxidative Stress / Q000502:physiology*