Frontotemporal lobar degeneration with writing disturbance mainly consisting of omission of kana letters

A right-handed woman developed pseudobulbar palsy and a particular writing disturbance mainly composed of omission of kana letters (OKL) at the age of 79, followed by gradual progression of generalized motor disturbance and mutism. She died at the age of 88. Postmortem examination revealed frontotemporal lobar degeneration. The precentral cortex and premotor area were the most severely degenerated among the affected frontal, parietal, and temporal lobes. The omission of kana letters has been recently reported as a characteristic feature of writing disturbance in Japanese amyotrophic lateral sclerosis (ALS). Our case indicates that OKL is not specific to ALS, and that the prefrontal and precentral cortices, common lesions between our case and ALS, are responsible for OKL. This case also shows that OKL can be caused by a pathomechanism independent from other types of writing error. The neurolinguistic analysis of our case suggests the disturbance of the moraic frame of words in the transcription process of morae into kana letters or kana-letter cards.