Researchers at the Feinstein Institute for Medical Research, Manhasset, NY, studied metabolic brain networks associated with Tourette syndrome (TS) and comorbid obsessive compulsive disorder (OCD) using PET imaging and spatial covariance analysis in 12 unmedicated patients and 12 age-matched controls. An abnormal TS-related spatial covariance pattern was characterized by reduced resting metabolic activity of the striatum and orbitofrontal cortex associated with relative increases in premotor cortex and cerebellum. In TS/OCD patients, a second metabolic pattern correlated with OCD and was characterized by reduced activity of the anterior cingulate and dorsolateral prefrontal cortical regions associated with relative increases in primary motor cortex and precuneus. The OCD pattern in individual subjects was correlated with severity of OCD. Different clinical manifestations of TS are associated with 2 distinct abnormal metabolic brain networks of potential value as biomarkers for assessing response to therapy. [1]

COMMENT. Metabolic brain network patterns differentiate subjects with TS from controls, as well as a second pattern that differentiates TS subjects with OCD from those without OCD. The brain networks involve regions associated with motor activity as well as those regions associated with behavioral changes (anterior cingulate and prefrontal cortex).

In an editorial, Dr Katie Kompoliti of Rush Med Sch, Chicago comments that this study identifies TS-related abnormal network patterns that encompass multiple interacting nuclei instead of isolated regions, a view of the whole "elephant," not just the trunk or tail [2]. She remarks that the study is limited by differences in gender mix of subjects (mainly male) and controls (mainly female). Other limitations include the age of subjects (all adults whose tics are usually severe), and the absence of additional TS comorbidities such as ADHD that might influence results.