Major depression is one of the most common forms of mental illness
in the United States with as many as 6% of the population
depressed at any given moment (point prevalence), and an estimated
10% of people becoming depressed during their lifetime
(lifetime prevalence). The symptoms of depression can be both psychologic
and physiologic, and are often subtle and unrecognized by patients
and health-care professionals. Symptoms may include intense feelings of
sadness and despair, sleep disturbances (too much or too little),
anorexia, fatigue, somatic complaints, and suicidal thoughts.
Depression is a heterogeneous disorder that has been classified
as (1) “reactive” or “secondary” depression
(most common), occurring in response to stimuli such as grief or
illness; (2) “endogenous” depression or major
depressive disorder, a genetically determined biochemical disorder
of depressed mood without any obvious medical or situational causes,
manifested by an inability to experience ordinary pleasure or to
cope with ordinary life events; and (3) depression associated with
bipolar affective (manic-depressive) disorder.
Physical therapists may encounter patients taking antidepressant
medications under a number of circumstances. Many patients who have
experienced life-changing disabilities become depressed and may
require medication for a limited time to control their depression.
Other patients may have a history of chronic depression not related
to their therapy diagnosis and require long-term treatment. Drugs
used in treating depressive disorders are highly effective in some
patients but only modestly, or not at all, effective in others.
No patients are cured. The major subclasses of antidepressant drugs
are outlined in Figure 19–1.
Major subclasses of antidepressants.
The amine hypothesis of mood postulates
that brain amines, particularly norepinephrine (NE) and (serotonin,
5-HT), are neurotransmitters in pathways that function in the expression
of mood. According to the hypothesis, a functional decrease in the
activity of such amines is thought to result in depression; a functional increase
in activity results in mood elevation. The amine hypothesis is largely
based on studies showing that drugs (such as reserpine) that deplete
central amines cause depression, and that most drugs capable of
alleviating the symptoms of a major depressive disorder enhance
the actions of the neurotransmitters 5-HT and NE in central synapses.
Difficulties with this hypothesis include the facts that (1) postmortem
studies do not reveal any decreases in the brain levels of NE or
5-HT in untreated patients suffering from endogenous depression;
(2) although antidepressant drugs may cause biochemical changes
in brain amine activity within hours, weeks may be required for them
to achieve clinical effects; (3) with chronic use, most antidepressants
ultimately cause a down-regulation
of amine receptors; and (4) at least one effective antidepressant,
bupropion, has minimal effects on brain NE or 5-HT.
While the amine hypothesis is undoubtedly too simplistic, it
has provided the major experimental models for the discovery of
new antidepressant drugs. ...