A large prospective study led by a longtime proponent of electroconvulsive therapy has found that the therapy causes permanent amnesia and permanent loss in cognitive ability sufficient to affect patients’ daily function, according to an article in the January issue of Neuropsychopharmacology.

"This study provides the first evidence in a large, prospective sample that adverse cognitive effects can persist for an extended period and that they characterize routine treatment with electroconvulsive therapy in community settings," the authors wrote.

The US National Institute of Mental Health (NIMH) estimates that more than 3 million Americans have received the therapy over the past generation. Previous studies had involved far fewer patients, typically 20 to 30, and evaluated only short-term effects of therapy.

The six-month study included 347 patients with major depression (unipolar or bipolar) or a depressive episode of schizoaffective disorder who received at least one therapy session and at least one post-session evaluation. Electroconvulsive therapy in the two months prior to enrollment was a criterion for exclusion.

Primary outcome measures were the Modified Mini-Mental State Exam, delayed recall scores from the Buschke selective Reminding Test, and retrograde amnesia scores from the Columbia University Autobiographical Memory Interview-SF; there were also a number of secondary outcome measures.

When post-therapy cognitive scores were compared with baseline scores, the entire sample had significant declines in many outcome measures. Typically, the greatest declines were seen in tests that assessed memory for autobiographical events, retention of recently presented information, global cognitive status, and simple reaction time.

Compared to baseline, there was significant improvement at follow-up in all measures excluding those involving reaction time and those assessing the sensitivity of continuous performance tasks.

Several factors involving therapy technique had different effects on outcome. Electrical wave form and electrode placement had marked effects. Sine wave stimulation correlated with more severe effects on reaction time immediately after therapy and at six months. Bilateral therapy caused severe, persistent retrograde amnesia compared with right unilateral therapy. A greater magnitude of post-therapy deficits was also associated with greater age, lower pre-psychiatric diagnosis intellectual ability, and female gender.