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1. What is Obsessive-Compulsive Disorder?

People with Obsessive-Compulsive Disorder (OCD) suffer from obsessions and compulsions. Obsessions are repetitive thoughts or images that the person finds intrusive and inappropriate, and that increase levels of anxiety. Compulsions are repetitive rituals (thoughts or actions) designed to counter obsessions and lower anxiety. For example, a person with obsessions about contaminations may wash their hands repetitively; or a person with obsessions about possible harm may check repeatedly.

While washing and checking are easily recognised, many people have more abstract symptoms such as having to pray over and over to get rid of blasphemous thoughts, or suffering from intrusive sexual thoughts, or having to hoard excessively. In addition to obsessions and compulsions, people with OCD may show avoidance behaviours; for example, the person with contamination concerns may simply stay indoors rather than risk going outdoors. Other people with OCD may take an extraordinarily long time to complete routine daily activities – this is a form of OCD known as ‘obsessional slowness’.

In the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV), OCD falls under that category of anxiety disorders. OCD often presents with other anxiety and mood disorders; in fact, a cross-national study found that the lifetime prevalence of Major Depressive Disorder among OCD patients range from 13 to 60% across seven countries. OCD mostly predates depression, suggesting that depressive symptoms usually occur in response to the distress and functional impairment associated with OCD. Many with this condition will seek treatment for depression or other secondary phenomena of OCD and will not reveal the sources of their problems unless specifically asked about.  Most people with OCD have good insight into their symptoms; they know that their concerns are excessive, even though they cannot help following through on compulsions to set their minds at ease.

2. What Causes Obsessive-Compulsive Disorder?

No one knows exactly what causes OCD. Although many processes remain unclear, there is increasing evidence that the cause of OCD lies in problems with the circuitry, structure and neurochemistry of the brain. Recent studies have demonstrated that people with OCD have different patterns of brain activity from normal individuals and those with other psychiatric disorders. In this way more evidence is added to the theory of a biological cause for OCD. Recent research findings have also shown that patients with OCD respond to a particular group of drugs, called the serotonin reuptake inhibitors. The neurotransmitter, serotonin, a naturally occurring compound in the brain involved in the transmission of nerve impulses, is thought to be a key factor in this disorder.

In females, a common age of onset is at the time of pregnancy or giving birth; hormonal interactions with brain chemicals are likely to play an important role in these cases. In addition, one subtype of OCD begins after certain infections, typically after a Streptococcal throat infection. This condition is termed PANDAS or Paediatric Autoimmune Neuropsychiatric Disorder Associated with Streptococcus. In such cases the body’s reaction to the Streptococcus bacterium mistakenly attacks a part of the brain called the basal ganglia. We know that the basal ganglia are important in humans with OCD because of several different kinds of studies. Amongst the first of these were early studies of neurology patients with different kinds of lesions of the basal ganglia where many of these patients developed OCD symptoms. The exact genes involved in OCD are not yet known, although they are likely to influence brain chemistry (and perhaps the brain chemistry of the basal ganglia in particular) in some way. This is a rapidly advancing area of research, and several candidate genes for OCD have already been proposed (e.g. catechol-O-methyl transferase).


3. Who Gets Obsessive-Compulsive Disorder?

OCD affects both males and females of all ages and ethnic groups. OCD commonly begins in adolescence or childhood, perhaps particularly in males. In females, another common ages of onset is at the time of pregnancy or giving birth; hormonal interactions with brain chemicals are likely to play an important role in such cases.

Once regarded as a rare psychiatric disorder unresponsive to treatment, OCD is now recognised to be a common problem affecting some 2 - 3% of the general population. OCD appears to occur at similar rates throughout the world. It usually lasts for many years during which time patient’s symptoms may very in severity and focus.

One subtype of OCD begins after certain infections; typically after a Streptococcal throat infection. In such cases the body’s reaction to the Streptococcal bacterium mistakenly attacks a part of the brain called the basal ganglia, resulting in sudden onset of OCD symptoms and / or tics.

On occasion, OCD is seen in people with various other neurological conditions, typically those that involve basal ganglia lesions. The basal ganglia are a group of structures that lie towards the centre of the brain, and that play a central role in learning and executing sets of motor sequences outside of awareness (e.g. initially learning to ride a bicycle requires conscious awareness, later these motor programs are carried out automatically).

Certain genes appear to play a role in causing OCD, and the condition is therefore somewhat more common in relatives of people with OCD or Tourette’s disorder than in the general population. The exact genes involved in OCD are not yet known, although they are likely to influence brain chemistry (and perhaps the brain chemistry of the basal ganglia in particular) in some way.