Obsessive compulsive disorder
OCD involves persistent, intrusive thoughts that compel one to perform a stereotyped action repeatedly. Although patients acknowledge how senseless their obsessions must appear, they cannot help but perform ritualistic behaviors to alleviate their anxiety. Dysfunction of circuits within the limbic system and orbitofrontal cortex has been postulated to underlie OCD. Surgery may be appropriate in patients with severe, chronic, refractory disease. Intervention is aimed at lesioning the anterior cingulum, subcaudate tracts, or anterior capsule.
OCD has an estimated prevalence of 2-3% and may severely impact a patient’s quality of life. It usually presents in childhood or young adults who may wash their hands excessively, pull out their hair, or engage in bizarre behaviors such as returning home multiple times to check that the oven is turned off. Neuro-imaging has implicated the cortical-striatal-thalamic circuit; in particular, PET imaging shows increased glucose metabolism in the orbital gyri. It is postulated that orbitofrontal –thalamic hyperactivity gives rise to obsessive thoughts.
Given the relatively low success rate of limbic system surgery, only appropriate patients should be selected for an invasive procedure. Symptoms should be present for at least five years. Indicators such as the Yale-Brown Obsessive-Compulsive Scale and Global Assessment of Function should be employed to gauge disease severity, with scores greater than 20 and less than 50 respectively. Lesions are made bilaterally under stereotaxic guidance. Anterior cingulotomy for OCD may require six to twelve weeks before any symptomatic improvement. Studies report that 25-56% of patients experience worthwhile change. Subcaudate Tractotomy targets the substantia innominata in order to disrupt fibers connecting the orbital cortex and subcortical structures. One rigorous study found that 50% of patients improved. These procedures may be combined in a limbic leucotomy, although results are necessarily superior. Anterior Capsulotomy may be performed by gamma knife, although this delays symptom relief. At three years follow-up 58% of patients in one study had responded.
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