What are the best known causes and treatments for apathy? Has any extensive research been done into what the most common causes of apathy are and are there any treatments with a highly reported success rate? If so, what are these?

For clarification of what apathy is, it is a state of desensitization, where subjects seem to strongly lack any observable moods, and have severely dampened feelings and/or emotions. One well known side effect is that apathetic people often struggle to motivate themselves to perform tasks.

(From wikipedia)


  Apathy is a lack of feeling, emotion, interest, and concern. Apathy is a state of indifference, or the suppression of emotions such as concern, excitement, motivation, and/or passion. An apathetic individual has an absence of interest in or concern about emotional, social, spiritual, philosophical, and/or physical life and the world.


Other questions specifically about apathy: What are the cognitive and neurological bases for apathy?

Some research about pathological apathy I was able to find: https://academic.oup.com/cercor/article/26/2/807/2367142/Individual-Differences-in-Premotor-Brain-Systems (here's also an article)
Main causes of Apathy

There are 2 main ways that Apathy can manifest itself, and that is either through a mental health condition, or a physical medical condition. (APA, 2013 p. 682) (IDC-10 Code: F07)

I will list some mental health causes and physical causes below, but the main way of dealing with the apathy would depend on the cause.

Treatment for apathy

The way to treat apathy would be to treat the root cause, where possible, through psychotherapy, psychiatric help and/or other agency support.

I emphasised root cause because where the initial cause found may be substance abuse for example, the substance abuse can be attributed to a different cause (the root cause) which could be a parent-child relationship problem or trauma.

Where apathy persists after treatment

If apathy remains after successful treatment of the root cause(s), then the problem will most likely lie with motivation.

You could look at the question on here about Theories of Human Motivation for information, or just look at various motivational courses, exercises and activities such as these activities.

Breakdown of Main Causes of Apathy

Mental health causes

This is not a full list, but includes,


Separation Axiety Disorder


  When separated from major attachment figures, children with separation anxiety disorder may exhibit social withdrawal, apathy, sadness, or difficulty concentrating on work or play.(APA, 2013 p. 192)

Major Depressive Disorder


  In major depressive disorder, the individual may avoid leaving
  home because of apathy, loss of energy, low self-esteem, and anhedonia. (APA, 2013 p. 221)

Neurocognitive Disorders (NCDs) such as Delirium


  Delirium is often associated with a disturbance in the sleep-wake cycle....The individual with delirium may exhibit emotional disturbances, such as anxiety, fear, depression, irritability, anger, euphoria, and apathy. (APA, 2013 p. 600)

Behavioral-Variant Major or Mild Frontotemporal NCD


  present with varying degrees of apathy or disinhibition. They may lose interest in socialization, selfcare, and personal responsibilities, or display socially inappropriate behaviors. (APA, 2013 p. 615)



Physical Problems Causing Mental Health Problems

This is not a full list, but includes,


Inhalant Intoxication
This can create


  Clinically significant problematic behavioral or psychological changes (e.g., belligerence, assaultiveness, apathy, impaired judgment) (APA, 2013 p. 538)

Opioid Intoxication
This can create


  Clinically significant problematic behavioral or psychological changes (e.g., initial euphoria followed by apathy, dysphoria, psychomotor agitation or retardation, impaired judgment) that developed during, or shortly after, opioid use. (APA, 2013 p. 546)

Other toxic, metabolic, traumatic, neoplastic, or infectious disorders that impair brain function and cognition


  Numerous neurological and other medical conditions may produce the clinically significant behavioral or psychological changes (e.g., belligerence, assaultiveness, apathy, impaired judgment) that also characterize inhalant intoxication. (APA, 2013 p. 540)

Major or Mild NCD due to Traumatic Brain Injury


  may be accompanied by disturbances in emotional function
  (e.g., irritability, easy frustration, tension and anxiety, affective lability); personality changes (e.g., disinhibition, apathy, suspiciousness, aggression); physical disturbances (e.g., headache, fatigue, sleep disorders, vertigo or dizziness, tinnitus or hyperacusis, photosensitivity, anosmia, reduced tolerance to psychotropic medications); and, particularly in more severe TBI, neurological symptoms and signs (e.g., seizures, hemiparesis, visual disturbances, cranial nerve deficits) and evidence of orthopedic injuries. (APA, 2013 p. 625)



References

American Psychiatric Association. (2013). Diagnostic and Statistical Manual of Mental Disorders (5th ed.). Washington, DC: American Psychiatric Publishing.