Rhesus monkeys with late-onset hydrocephalus differ from non-impaired animals during neonatal neurobehavioral assessments: six-year retrospective analysis.

BACKGROUND AND PURPOSE: A recent case study indicated that a hydrocephalic rhesus monkey had abnormal response patterns in a standardized neonatal primate assessment. We conducted a retrospective study to determine whether this assessment could also differentiate neonatal rhesus monkeys that appeared normal but developed signs of hydrocephalus later in life from neonates with normal development and no evidence of hydrocephalus. METHODS: One-hundred eighty-two rhesus monkeys were assessed on postnatal days 7, 14, 21, and 30. As neonates, clinical signs of hydrocephalus or other illnesses were not evident in any animal. Six monkeys developed signs of hydrocephalus between 5 months and 5 years of age, and each received confirmed diagnoses of hydrocephalus at necropsy. RESULTS: Compared with colony norms, the monkeys that developed hydrocephalus had diminished orientation abilities, more muscle tension, less behavioral evidence of distress, and more pronounced responses to some reflex-evoking stimuli, and difficulty in self-righting (day 7 only). Discriminant function analysis comparing the hydrocephalic animals with a matched control group provided a high probability of correct group assignment at days 7, 14, and 21. CONCLUSIONS: Some as yet undetermined factor may predispose some monkeys to develop hydrocephalus, which may also be reflected in different scores on neurodevelopmental test items during early infancy.