Depression is one of the most common mental illness; as a matter of fact it has been said to be the common cold of mental disorders- almost everyone gets it one time or the other. ~57 million people, in India itself, are estimated to suffer from depression. However, depression thought currently diagnosed and classified as one entity, is not a homogeneous illness in practice. There are different sub-types of depression.
But first lets recall the symptoms of depression. These I have drafted in ABCD terms for easy recall. Its also useful to think of symptoms as tings that are added to normal experience (the positive symptoms if you may) and things that are missing (the negative symptoms) – although this distinction is usually made in case of schizophrenia. Also important to remember is that at least 5 of the following symptoms need to be present for at least 2 weeks for a clinical diagnosis.
- Affective: Presence of affect : Low mood or prolonged sadness is an affect that is present, and required for diagnosis of depression. The sad emotion is something that has been added.
- Affective : absence of affect: Typically one feels pleasure while doing small everyday activities like having a cup of coffee in the morning. A depressed person doe snot feel pleasure form such activities and suffers from Anhedonia – on the inability to experience pleasure. Here something has been taken away from the normal experience.
- Behavioral: presence of behavior: Depression results in abnormalities in sleep, appetite and body weight. When excess sleep (hypersomnia) or excessive appetite or psychomotor agitation or weight gain appears that can be a symptom of depression.
- Behavioral: absence of behavior: Depression results in abnormalities in sleep, appetite and body weight. When loss of sleep (insomnia ) or less appetite or psychomotor retardation or weight loss appears that can be a symptom of depression.
- Cognitive: presence of thoughts/ beliefs: dysfunctional beliefs are present in depressed people including worthlessness and guilt. These thoughts do not make or dominate the normal thought repertoire of most people.
- Cognitive: absence of cognitive capacity: Depressed people are not able o think or concentrate; they are also indecisive. All these are cognitive capacities that are lacking or compromised as compared to normal folks.
- Drive: presence of motivation : Here I am tempted to put suicidal ideation and attempts: a drive to escape from life and end it. Something again not normally found in normal people, but a motivational force for the depressed person.
- Drive: absence of motivation: Anergia (loss of energy) and fatigue go here: one feels drained and unwilling and unable to do anything. Again normal people have decent amount of energy or drive and this is somewhat deficient in the depressed person.
Now that we know what depression looks like, and how its diagnosed (above is as per DSM-5 criteria), what can we conjecture about the heterogeneous nature of depression? One useful way to think about depression sub-types is to think of whether it is predominantly Affective in nature, or is it Behavioral or Cognitive or Motivational. Could this differentiate among meaningful sub-types?
For this it may make sense to refer to this paper [pdf] about which I blogged some time back. Please do read my blog or the original paper. The authors identified two dimensions of Anhedonia and Anxiety and identified four neural subtypes of depression. They replicated the four subtypes in Generalized Anxiety Disorder (GAD) too which is closely related to depression.
It is instructive to note that in that paper, that Anhedonia axis is affect related while Anxiety axis is more cognitive. To me the four subtypes appear as equivalent to whether the predominant symptoms are affective (subtype 3), or whether they are behavioral (subtype 1?) or cognitive (subtype 4?) or motivational (subtype 2).
Irrespective of what the underlying subtypes may refer to, its clear that depression is heterogeneous and the better we identify and start treating the subtypes differently the better it will be for those suffering from depression.