Palinacousis—Evidence to suggest a post-ictal phenomenon
Palinacousis is a paroxysmal auditory illusion in which perseveration of an external auditory stimulus occurs after cessation of the stimulus. The subjects recognize the illusory nature of this experience, which is often a fragment of the last sentence they heard. Palinacousis has been reported in only a few documented cases. It has been described as an aura, a component of complex partial seizures, and a post-ictal event. We put forward evidence demonstrating palinacousis as a post-ictal event. A 68-year-old woman presented with an acute sensory aphasia, and an EEG showed frequent epileptiform discharges from the left temporo-parietal region. MRI showed an enhancing mass in the left inferior parietal lobule that was consistent with a metastasis. A CT scan of the thorax later showed an enhancing mass in the left lung that was determined to be an invasive non-small cell carcinoma. Treatment with levetiracetam resulted in loss of epileptiform activity on EEG and resolution of aphasia, but soon afterward, she started complaining of recurrent auditory illusions in her right ear. These consisted of phrases from the ends of sentences she heard. Continuous EEG monitoring during her auditory symptoms showed intermittent left temporal slowing but no epileptiform discharges or electrographic seizures. An FDG-PET scan with the glucose uptake phase during episodes of auditory illusions revealed hypometabolism of bilateral medial temporal cortices and increased uptake in the metastatic tumor. A systematic review identified 14 cases with palinacousis since 1981. Cases prior to that were excluded due to the lack of sufficient data. We propose that palinacousis is a “negative” phenomenon, at least in some individuals. It occurs with a loss of function of a region of the brain that normally suppresses auditory perseveration.