Early stages of the Rett syndrome and infantile neuronal ceroid lipofuscinosis--a difficult differential diagnosis.

The Rett syndrome (RS) and infantile neuronal ceroid lipofuscinosis (INCL) are known clinically to present with quite similar manifestations in the very first stages of disease. Ten girls, born 1982-85, from the Swedish series of RS, were compared with 6 children with biopsy-confirmed INCL, deriving from 4 families, as to neurodevelopmental, neurological, ophthalmological, neurophysiological, and CT data. The rapid regression at 1-2 years of age with loss of acquired fine motor skill, learned words, and communication were found to be inseparable between the diseases, as were the successively developing hand and finger stereotypies. Early clues for differential diagnosis were the appearance of transient drop spells, loss of head control, and irregular myoclonias in INCL, flattening of the EEG, early cortical atrophy indicated at CT, and particularly abnormal ERGs. For accurate diagnosis of INCL a biopsy with characteristic EM findings of "snowball" aggregates is a necessity. After 2 3/4-3 years of age, a clinical differentiation was possible in all cases, with visual failure and rapidly decreasing motor ability, head control deterioration, hyperexcitability, and trunk-limb extension tonus being characteristic for INCL.