New onset focal weakness in children with Down syndrome.

New onset focal weakness is relatively common in patients with Down syndrome (DS), and has broad differential diagnosis. Ten cases of new onset focal weakness in patients with DS were encountered or are currently being followed in two DS clinics, with a combined population of patients of approximately 850, for a clinic population prevalence of 1.2%. The median age at presentation was 4 years old (range 1 month-44 years). The causes of new onset focal weakness were: stroke from Moyamoya disease (two patients); stroke from vaso occlusive disease (one patient); stroke from venus sinus thrombosis (one patient); traumatic subdural hematoma (one patient); brain abscess (one patient); spinal cord injury (SCI) from cervical spinal stenosis (two patients); SCI from atlantoaxial instability (AAI) (one patient); and brachial plexus injury (one patient). Of the 10 patients with focal weakness, 8 had potentially treatable conditions, and 5 had surgery. The differential diagnosis of new onset focal weakness in DS is broad, with diseases reported involving all levels of the nervous system from brain to muscle. For some diagnoses, expeditious diagnosis may improve outcome.