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Table 1 Characteristics of depression and sickness behavior.

From: Depression and sickness behavior are Janus-faced responses to shared inflammatory pathways

 

Clinical depression

Sickness behavior

Basic symptoms

Depressed mood most of the day

Decreased interest or pleasure in almost all activities

Anorexia, and/or significant weight loss or weight gain

Insomnia or hypersomnia

Psychomotor agitation or psychomotor retardation

Fatigue or loss of energy

Decreased ability to think or concentrate

--

Disinterest in social interactions

Anorexia and weight loss; no weight gain

Sleepiness

Reduced locomotor activity; no agitation

Lethargy

Failure to concentrate

Existential symptoms

Feelings of worthlessness or guilt

Suicidal ideation or behavior

--

--

Melancholic dimension

A distinct quality of depressed mood (anhedonia)

Non-reactivity

Diurnal variation

Early morning awakening

Psychomotor retardation

Excessive weight loss

Reduced intake of sweetened milk (anhedonia)

Behavioral inhibition

--

--

Reduction of locomotor activity and exploration

Important weight loss

Anxiety dimension

Tension; physiological behavior; respiratory symptoms; genito-urinary symptoms; autonomic symptoms; anxious behavior at interview (general)

Anxiety

Physio-somatic dimension

Flu-like malaise; aches and pain; muscle tension (in some of the patients)

Malaise and hyperalgesia (key symptoms of sickness)

Pyrexia

Slightly increased body temperature

Pyrexia

Onset

Course

Insiduous

Waxing and waning or relapsing-remitting

Chronic

Sensitization of episodes

Seasonal variation

(Hypo)manic episodes

Acute onset

Acute adaptive response, maximal 19 to 43 days

May be prolonged, but then is maladaptive

--

--

--

Pathways

(Sub)chronic inflammation with increased PICs

CMI activation

Sensitization of inflammatory and CMI pathways

Activation TRYCAT pathway

O&NS

Damage by O&NS

Autoimmunity

Neuroprogression

Acute inflammation with increased PICs

Activated

--

Maybe activated TRYCAT pathway

Unknown but probably yes

--

--

--

Triggers

Multiple, not well defined

Psychosocial stressors, medical inflammatory illness, neuroinflammatory disorders, inflammatory conditions

Acute, highly defined

Acute pathogens and tissue injury

 

Episodes tend to become autonomous from trigger

Is always a response to a defined trigger

General

Inflammation-related chronic progressive disorder

Inflammation-induced adaptive behavioral response that is conserved through evolution

PICs' Janus-face

Bad 'chronic' side: a chronic disorder with positive feedback loops between (neuro)inflammation and (neuro)degenerative processes

Good 'acute' side: supports inflammation, redirects energy to immune cells, conserves energy and prevents negative energy balance, helps eradicating the trigger, and has anti-inflammatory effects

  1. CMI, cell-mediated immune; O&NS, oxidative and nitrosative stress; PICs, pro-inflammatory cytokines; TRYCAT, tryptophan catabolites.