Two patients with obsessive compulsive disorder, which made one of them obsessively clean her house and the other check his locks for up to three hours a day, have been cured by electrodes implanted in their brain, it is reported today.

The patients underwent brain surgery not because of their compulsive behaviour but to alleviate the symptoms of Parkinson's disease. Their doctors say, in a letter to the Lancet medical journal, that two weeks after the electrodes were implanted the compulsions had gone.

There is no easy cure for obsessive compulsive disorder, which the French scientists describe as "a major challenge" to treat. Relief through drug treatment can be partial and does not last when the drugs are stopped.

Their two patients had a long history of compulsive behaviour. One, a 51-year-old woman, had suffered from OCD for 33 years. Symptoms included repetitive cleaning, arranging and rearranging bottles on a bathroom shelf, and a terror of being found dead in a dirty house.

The other, a 50-year-old man, had exhibited obsessive behaviour for 40 years - predominantly by checking locks. In adulthood his symptoms lessened, but they became worse with the onset of Parkinson's disease.

The first patient had electrodes implanted in her brain to reduce the symptoms of Parkinson's disease in December 2000, and the second in June last year.

The electrodes were implanted in a part of the brain known as the subthalamic nucleus, which has been implicated in OCD.

In both cases the Parkinson's symptoms improved and the compulsions stopped. The woman "claimed she was more pleased about the disappearance of her OCD symptoms than about the moderate improvement in Parkinsonian disability," say Luc Mallet and colleagues from the Hopital de la Pitie Salpetriere in Paris.

The authors say the cases raise the possibility that high frequency stimulation of part of the brain could help people with severe OCD.