We describe a patient with a complex neuropsychiatric disorder who presented a severe and diffuse cerebral glucose hypometabolism on 18F-FDG PET initially which, in the clinical setting, was suspicious of an advanced neurodegenerative disease. Further evaluation suggested a major depressive episode with agitation and poor response to medication. Electroconvulsive therapy (ECT) brought excellent results. A follow-up cerebral 18F-FDG PET was completely normal, thus illustrating the potential for complete recovery and normalization of brain metabolism in major depressive episode following ECT. It also shows the risk of false interpretation of brain PET in patients with depression.