28 Functional Neurosurgery for Obsessive-Compulsive Disorder
Abstract
Obsessive-compulsive disorder (OCD) affects two to three percent of the population, and a third of OCD patients are poorly responsive to all conventional treatments. For a subgroup of such OCD patients, psychiatric neurosurgery-lesions or deep brain stimulation (DBS)- is an option. This chapter provides an overview of the most common neurosurgical techniques for OCD, with a focus on outcomes and safety. In addition, detailed information about the typical processes used to evaluate potential patients is included.
Obsessive-compulsive disorder (OCD) affects two percent of the population, and the World Health Organization ranks OCD as one of the 10 most disabling conditions. 1 OCD is characterized by obsessions, which are intrusive, persistent, repetitive thoughts that cause distress, as well as compulsions, which are physical or mental acts that are carried out in an aim to reduce the distress associated with the obsessions. A third of OCD patients are poorly responsive to all conventional treatments. 2 For a subgroup of such OCD patients, neurosurgery-lesioning or deep brain stimulation (DBS) are an option.
28.1 OCD Neurocircuitry and Relation to Neurosurgery
Abnormalities in the cortico-striato-thalamo-cortical circuitry are evident in multiple psychiatric disorders, including OCD. 3 These neuroanatomical models of OCD that have been developed from functional neuroimaging are consistent with the empirically-developed targets chosen for lesions or DBS. Decades of research have consistently demonstrated that lesions within CSTC circuitry reduce OCD symptoms. While studies have shown clinical improvement after these procedures, the mechanism for such improvement remains unknown.
28.2 Patient Selection
Standards for psychiatric neurosurgery have included strict criteria for patient selection. Approval is completed through a multi-disciplinary committee after an extensive psychiatric and medical evaluation, including review of all prior treatments. In some countries, governmental approval is required before surgery. Though exact guidelines may differ slightly across sites, approval for surgery is generally based upon: (1) Patients with severe, treatment-resistant OCD, of at least 5 years in duration, which has caused functional interference and poor quality of life. Severity is based on the YBOCS, with a score over 26 to 30; (2) Patients who have failed all conventional treatments, and prior treatment trials must be clearly documented and judged as adequate, which often requires interviews with prior treating clinicians. Medication trials (duration of at least two months) include trials of a serotonin reuptake inhibitor (often high dose trials are needed in OCD), as well as a neuroleptic trial and trials of clomipramine and clonazepam. These should also include at least 20 sessions of exposure and response/ritual prevention (ERP) (3) Patients with current comorbid substance abuse or severe personality disorders may not be appropriate candidates. The ability to comply with follow-up treatments should also be judged, particularly with DBS, where the pulse generators require frequent charging and patients need to return for frequent post-surgical visits; (4) Significant neurological conditions (e.g. extensive white matter disease, stroke) may be a contraindication. Medical conditions that may increase surgical risks may also be a contraindication. Pre-operative work-up includes an MRI, neurological exam, and neuropsychological assessment; (5) With both ablative and neuromodulatory procedures, patients should continue to receive treatment with a psychiatrist and a therapist skilled in ERP. The majority of patients remain on psychiatric medications post-surgery, though there may be a decrease in the number of prescribed medications. In the case of DBS, access to specialized psychiatric neurosurgery teams is recommended for clinical monitoring and device adjustment. Patients will need continued pulse generator replacements, and future costs, particularly of DBS, should be considered. Long-term follow-up is essential to track clinical change and adverse effects; (6) Patients should always be able to provide appropriate consent for a neurosurgical procedure. Presently, these procedures are reserved for those 18 years of age or older; (7) Though not mandatory, family support is recommended and likely contributes to improved outcomes after surgery.
28.3 Ablative Procedures
Ablative procedures were largely developed empirically, with targets often derived from early work on animals. There are four most commonly used ablative procedures: subcaudate tractotomy (SCT), anterior cingulotomy (ACG), limbic leucotomy (LL), and anterior capsulotomy. All procedures use stereotactic methods, though with different techniques. Thermolesions involve craniotomy, insertion of an electrode, and radiofrequency heating of the tip to cause a lesion. Approximately two decades ago gamma knife radiosurgery was also introduced.
28.3.1 Subcaudate Tractotomy
In SCT, lesions are placed in the substantia inominata, ventral to the caudate, and is intended to interrupt tracts between the OFC and subcortical limbic structures. The procedure is not commonly used except as part of a LL (discussed below), and is usually done with thermocoagulation. Outcomes vary considerably, and success rates range from 33 to 67 percent. 4 Complications include transient disorientation, seizures, fatigue, and weight gain. There has been one reported death due to a neurosurgical complication. 4 Post-operative cognitive impairments have not been reported, but research is limited. 5
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