A 43-year-old man presented with an 18-month history of acute-onset cy
clical behavioural change affecting mood, appetite, sleep, and energy
levels. This had followed an initial episode of transient drowsiness w
hich lasted 24 hours. On examination, there was some evidence of visua
l memory and frontal lobe deficits. A brain CT scan showed bilateral t
halamic infarcts and a brain SPECT scan showed bilateral hypoperfusion
of the frontal lobes. To our knowledge, this is the first reported ca
se of thalamic infarction associated with acute-onset cyclical affecti
ve psychosis with clinical and neurophysiological features of frontal
lobe syndrome. The case also highlights the possible role of thalamo-f
rontal circuits in the pathogenesis of the Kleine-Levin syndrome.