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Day # 91: OCD - The “who” and the “why”

Welcome to day two of our theme on obsessive compulsive disorder (OCD) and related disorders. Today we are going to go one level deeper and overview some epidemiology, risk factors, and the typical course and prognosis of OCD.

Today’s Content Level: Beginner, Intermediate


•Prevalence = proportion of individuals who have a condition at a particular period of time

•Incidence = proportion or rate of individuals who newly develop a condition during a period of time

  • Prevalence: 12-month prevalence of OCD is between 1-2%. Lifetime prevalence ~2-3%.

  • Gender: women and men are about equally affected. Males have an earlier age of onset than females.

  • Age: average age of onset is ~20 years old. A bimodal distribution of the incidence of OCD has been suggested and studies have found two peaks in age of onset at 11-14 years and at 20-29 years. Onset after age 35 years is unusual but does occur (<15%).

  • Race: prevalence is similar across racial groups.

  • Suicide risk: contrary to long-standing beliefs, individuals with OCD are ten times more likely of dying by suicide than the general population. Suicidal ideations occur in ~50% and suicide attempts in as many as ~25% of individuals with OCD.


•Biological, environmental, psychosocial, and genetic factors are all important in obsessive compulsive disorder.

Genetic 2

  • Significant genetic component with higher rates of OCD in first-degree relatives (3-5 times higher than the general population). Even higher risk among relatives with onset in childhood or early adolescence.

  • Higher concordance rate in monozygotic (0.57) vs dizygotic (0.22) twins.

  • There is also a higher rate of OCD in first-degree relatives with Tourette's disorder.

Other known risk factors include:

  • Childhood maltreatment: correlation with physical, sexual, and emotional abuse. Known risk factor for many psychiatric conditions.

  • Infectious / Autoimmune: some children may develop acute onset obsessive-compulsive symptoms in the context of infection with group A streptococci or other triggers (viral infections, drugs, or metabolic abnormalities). These conditions are known as PANDAS (pediatric autoimmune neuropsychiatric disorder), PANS (pediatric acute-onset neuropsychiatric syndrome), or CANS (childhood acute neuropsychiatric symptoms). We will discuss these topics later in this theme.

  • Temperament / Personality: certain traits are possible risk factors and include behavioral inhibition (tendency towards distress/nervousness/withdrawal in new situations) and higher negative emotionality.

Pathophysiology 3

  • Neurotransmitters: dysregulation of serotonin is hypothesized and most of the supporting data is from clinical drug trials. Data shows that serotonergic drugs are most effective in treating OCD. Past research also shows glutamate and dopamine involvement. Currently, there is less evidence for dysfunction of the noradrenergic system.

  • Neuroanatomy: numerous lines of research support a role for cortico-striatal-thalamo-cortical (CSTC) circuits in OCD. Dysfunction in the orbitofrontal cortex, anterior cingulate cortex, and striatum (caudate nucleus, putamen, and globus pallidus) have been most strongly indicated. These findings have been supported by brain imaging studies (structural, PET, fMRI) and neurosurgical treatment. See this article for a more thorough review.


  • Onset: typically gradual, but sudden onset of symptoms can be seen. Some sources even report that more than half of patients with OCD have sudden onset of symptoms that first occur after a stressful event (ex: pregnancy, death of relative).

  • Course: a chronic course, spanning over several decades, with waxing and waning symptom severity, is typical of OCD. In contrast some patients do have an episodic course (~25% of cases according to one study 5) where symptoms are only present during an episode and during the remaining time symptoms remit with or without treatment. It is unclear what the symptom-remission interval should be to qualify for an episodic course in OCD.

  • Prognosis: spontaneous (untreated) remission rate among adults is ~20%. With treatment ~20-30% have significant improvement in their symptoms and 40-50% have moderate improvement.

  • Predictors of poor prognosis: yielding to (rather than resisting) compulsions, onset of symptoms during childhood, bizarre compulsions, the need for hospitalization, coexisting MDD, delusional beliefs, and coexisting personality disorder (especially schizotypal).

  • Predictors of good prognosis: good social/occupational adjustment, the presence of a precipitating event, and episodic nature of symptoms.


Obsessive compulsive disorder (OCD) is highly co-morbid with other psychiatric disorders as well as general medical conditions. There are multiple reasons for this including shared genetic and environmental vulnerabilities, potential causal relationships, and consequences of treatment.

  • Anxiety disorders (~75%) are common (generalized anxiety disorder, panic disorder, social anxiety disorder, and specific phobia)

  • Major depressive disorder (~60%)

  • Alcohol use disorder

  • Tic disorders (~30%) (ex: Tourette's)

  • Eating disorders

  • Personality disorders


I hope today's lesson provided a nice overview about the "who" and the "why" of OCD. In our next post we will discuss clinical pearls for OCD.

Resources for this post include Pocket Psychiatry, Kaplan and Sadock synopsis of psychiatry, DSMV, and First Aid For the Psychiatry Clerkship as well as the articles referenced in the post. I highly recommend adding these to your psych library.

Bullet Psych is an Amazon Associate and we receive a small commission if you use our links.

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