Transient memory impairment and transient global amnesia induced by photodynamic therapy

Photodynamic therapy (PDT) is a commonly used and effective treatment option for nonmelanoma skin cancer. Apart from local side-effects such as pain, oedema and erythema, no major adverse events occur in the majority of cases. Here we report on five patients who developed memory deficits such as transient global amnesia immediately after PDT for actinic keratosis. All PDT treatments were performed according to standard therapy protocols. The reported patients had a memory gap for the entire procedure, as well as for the consecutive emergency medical care. Other common neurological causes such as stroke or epileptic seizures were excluded. No focal neurological deficits were detectable. The symptoms had a fairly rapid onset following red-light illumination and were reversible without sequelae within 1-24 h. No correlation of the condition and pain during the illumination could be revealed. Magnetic resonance imaging of the brain revealed punctuated lesions in the hippocampus as a potential morphological correlate in one patient. The association between amnestic syndromes and PDT is novel and has not previously been reported. Even though PDT is considered a safe treatment modality, the possibility of neurological adverse events, albeit rare, should be kept in mind.