TMS and OCD
Obsessive compulsive disorder (OCD) is a severe condition, which, in patients most severely affected, current medication and behaviour therapies fail to control. Advancing knowledge of brain circuit involvement has potential treatment implications.
The use of transcranial magnetic stimulation (TMS) to probe possible neuroanatomic and neurophysiologic variables of this disorder is invaluable, and the knowledge gained from such studies may provide advances in treatment (Greenberg et al. 2000 [1]).
Neurophysiological abnormalities
A study by Greenberg et al. (2000[2]) reported significantly decreased intracortical inhibition (ICI) at interstimulus intervals from 2 to 5 msec. They also found decreased active and resting motor evoked potential threshold in the OCD patients, another indication of increased cortical excitability. Neither abnormality appeared medication related. The decreases in ICI and motor threshold were greatest in OCD patients with comorbid tics, but remained significant in patients without tics. The authors concluded that the data suggests abnormal cortical excitability in OCD and stated that these findings are congruent with the hypothesis that Tourette's syndrome and OCD are analogous disorders with overlapping dysfunction in corticobasal circuits. Patients with tic-related OCD may have more abnormal motor cortex excitability than OCD patients without tics (Greenberg et al. 2000 [2]).
Treatment
In most cases, treatment is initiated with an SSRI. When dealing with patients who do not respond to one SSRI, alternatives include switching to a different SSRI, combining another medication or behavioural therapy with SSRI therapy, considering novel or experimental drug treatments or employing nonpharmacologic biological approaches, such as electroconvulsive therapy, neurosurgery or rTMS (Goodman 1999).
Many studies have attempted to prove that rTMS alone is successfully able to treat OCD, but the results have frequently conflicted, with some showing no improvement after treatment with rTMS (eg. Sachdev et al. 2007) and a number of trials showing that rTMS can improve the symptoms of OCD (eg. Mantovani et al. 2010). This could be as a result of varying treatment paradigms and differing stimulation locations.
References
- Goodman, J Clin Psychiatry, 1999.
- 1. Greenberg et al., Psychiatr Clin North Am, 2000.
- 2. Greenberg et al., Neurology, 2000.
- Mantovani et al., Int J Neuropsychopharmacol. 2010.
- Sachdev et al., Psychol Med, 2007.
