It's all in your head: Brain inflammation in OCD

18 August 2017
Posted by Caroline Stoten.

Disabling and disruptive to the lives of sufferers, obsessive compulsive disorder (OCD) affects around 740,000 people in the UK, who battle obsessive, anxious thoughts and compulsive behaviours every day. But why...? 

Despite being listed as one of the top ten most debilitating illnesses by the World Health Organisation (WHO), the physical cause of OCD is unclear. This lack of understanding has enabled the trivialisation of this illness and makes it difficult to develop new treatments. Recent research has uncovered evidence of inflammation in the brains of people with OCD, and specifically in regions associated with behaviour. The severity of the inflammation is also in step with the severity of the symptoms: those with more severe OCD show higher levels of inflammation. These exciting findings highlight the physical nature of mental illness and may lead to new treatments.

Warning signs

Inflammation is an immune response which can be triggered by the presence of a foreign entity, such as an infection, or by an over-active immune system. In both cases, blood flow to an affected area increases. When this occurs in the brain it is called neuroinflammation, and the activity of cells called microglia, which protect our brain and spinal cord from infection, can be used as a proxy marker that it's occurring. During inflammation, microglia produce an immune response protein called ‘translocator protein’, or TSPO. The presence of high levels of TSPO in specific areas of the brain can therefore pinpoint areas of inflammation.

Using a radioactive probe for TSPO, scientists analysed the levels of brain inflammation in OCD-suffering and healthy study participants. Significantly higher levels of inflammation were visible in the brains of OCD sufferers compared with the healthy controls. More specifically, higher levels of inflammation were found in regions of the brain that form a system called the cortico-striato-thalamo-cortical (CSTC) circuit, which is know to play a role in behaviour. The affected areas included the dorsal caudate, orbitofrontal cortex, thalamus, ventral striatum, dorsal putamen and the anterior cingulate cortex, and these findings indicate that inflammation of these areas of the brain is linked to - and may even lead to - OCD. What’s more, the higher the levels of inflammation present in the orbital frontal cortex, the more severe a person’s OCD was likely to be, as measured by the Yale-Brown scale, which us used to gauge OCD severity.

Targeting treatments

Despite treatments for OCD being available, such as cognitive behavioural therapy (CBT) and the use of anti-depressants, these don't work for everyone. Further evidence that inflammation contributes to OCD could open up an entirely new treatment option for OCD sufferers, perhaps in the form of drugs that target the immune system, which are already used for the treatment of other illnesses such as inflammatory bowel disease and some cancers. The Yale-Brown scale was used in this research to specifically measure the distress caused when an OCD patient is prevented from carrying out a compulsion. Since a patient’s position on the Yale-Brown scale is correlated with the level of inflammation in their brain, immunomodulatory drugs may be particularly effective for OCD sufferers that experience exceptional distress associated with compulsions. Furthermore, sufferers which are more likely to benefit from such treatment could be identified by the presence of inflammation-associated proteins in their blood, thus enabling a form of "personalised medicine" like that employed in some cancer treatments.

This is not the first time that OCD has been linked to the body’s immune response. Neuropsychiatric disorders, including OCD and tic disorders, can develop suddenly in children infected with a subgroup of Streptococcal bacteria. This results in the production of antibodies that attack part of the brain called the basal ganglia. This phenomenon is called ‘Paediatric Autoimmune Neuropsychiatric Disorder Associated with Streptococcal infection’, or PANDAS, and, although this is largely specific to children and implicates a different area of the brain, is a further example of how the immune system might be involved in OCD.

OCD is a physical illness

Obsessive compulsive disorder is one of the most misunderstood and trivialised illnesses. This is partly due to OCD being widely used as a synonym for neatness, with many non-sufferers claiming to have OCD. This trend is damaging to sufferers, who may avoid speaking out or seeking help as a result. An understanding of how OCD affects the brain is therefore an important step in targeting this mental health stigma. As a sufferer of OCD myself, these findings are very encouraging, not least because they provide evidence that OCD is accompanied by a physical change in the brain. A large barrier for sufferers of mental illness is the common assumption that their affliction is "all in their head" and that they should simply "snap out of it". It is my hope that findings like these could be used as a tool to educate people that mental illness can be as physical as many other injuries or diseases. Above all, it needs to be taken seriously.

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