LEC 18: Obsessive compulsive and related disorders

What is Obsessive Compulsive Disorder and related disorders?

• characterized by the presence of obsession and/or compulsions

• differ from normative rituals, must be excessive

Diagnostic criteria for OCD

• presence of obsession, compulsion, or both:

  • obsessions are defined by:

    • recurrent and persistent thoughts, urges, or images that are experienced as intrusive and unwanted

  • compulsions are defined by:

    • repetitive behaviours (e.g. hand washing) or mental acts (e.g. repeating words silently) that the individual feels driven to do and according to rules that must be applied rigidly

    • aimed at preventing or reducing anxiety or distress

• must be time-consuming or cause significant psychological distress

OCD is a clincally heterogenous disorder

• the Yale-Brown Obsessive Compulsive Scale (Y-BOCS) assesses presence of OCD

• 4 discrete dimensions of the disorder (symmetry, taboo thoughts, contamination, hoarding)

Prevalence of OCD

• affects about 2% of the population

• more boys diagnosed with childhood onset; more females with adult onset

• suggests distinct neural circuitry and/or distinct genetic/etiological origins

Neural basis of OCD

• Involves a circuit connecting the prefrontal cortex to subcortical regions (basal ganglia and thalamus) that regulate sensory-motor behavior, known as the CSTC.

• In OCD, glutamatergic signals from the PFC normally excite the striatum, inhibiting the GPi via GABA and exciting the PFC through thalamic disinhibition. This process forms a direct pathway.

• In OCD, the cortex is hyperactive

• In OCD, the striatum, which filters information, is impaired, allowing intrusive thoughts to become obsessions.

• Under-inhibition of the thalamus causes hyperactivation of the PFC.

The cortico-striato-thalamo-cortical (CSTC) circuit

• a ‘communication loop’ that connects different brain areas to process information. Signals travel between:

  • The Cortex: the ‘thinking’ part of the brain that processes information like touch, sight and decision-making

  • The Thalamus: a ‘relay station’ that helps send sensory and motor information to the right places

  • The Striatum: part of the basal ganglia, involved in controlling movement and habits

Etiology of OCD

Genetic:

• OCD is familial due to several gene variants that have additive effects on disease

• 3 principal candidate neurotransmitter systems: serotonin, dopamine and glutamate

Environmental:

• perinatal events

• stress

• trauma

• neuroinflammation

Treatment for OCD

• average range from symptom onset to treatment is 8 years

• typically prescribed SSRIs

• successful cognitive-behavioural therapy shows reduced metabolic activity in the PFC, and parts of the basal ganglia