The subject presented with intellectual decline followed by progressive muscle weakness of the bilateral upper limbs when he was 60 years old. He had a point mutation (methionin-valine) at 129 prion protein codon. He died at the age of 63 and necropsy revealed bilateral frontal lobe atrophy. The frontal cortex showed neuronal cell loss in layers II and III with spongiform change. Reusche silver impregnation technique for beta-peptide combined with ubiquitin immunostaining revealed perineuronal structures encircling degenerated neurons and ubiquitin-immunoreactive (IR) dot-like deposits. They were distributed particularly in the temporal neocortex and entorhinal cortex. They differed from either classic senile or diffuse plaque by the absence of amyloid core in the center and of amyloid fibrils. Ubiquitin-IR materials were also found as neuronal inclusions in the hippocampal granular cells. Nigral degeneration and neuronal loss in the hypoglossal nerve nucleus and in the anterior horn of the spinal cord were also found and spinal cord motoneurons had Bunina body inclusions. The clinical features and pathological findings were consistent with non-Alzheimer dementia with status spongiosus and neuronal cell loss. The unusual perineuronal structures found in our case might be a specific cellular pathology of dementia of the frontal lobe type.