Discussion. This is the first report documenting the association of high-dose PYD use during pregnancy with microcephaly and CNS injury. Known causes of microcephaly were excluded in our patient, who did not develop any signs of a degenerative disorder. The mild ventriculomegaly demonstrated on brain MRI and, clinically, his bilateral ankle clonus attest to the presence of CNS injury.

The patient’s mother consumed more than 40 mg/kg of PYD per day, whereas the recommended dose is less than 10 mg/kg. 1 PYD amounts higher than 900 mg/day have not reported during pregnancy. 3 This prudent dosing limit is borne out in animal studies. Rat pups exposed to 30 mg/kg/day of PYD were smaller than unexposed littermates and had abnormal ossification in the cervical vertebrae. 2 Our patient’s microcephaly, prematurity, and growth retardation has not been seen in patients with NMG, even in those with atypical features. 4 Drugs, such as phenytoin and ethanol, that affect the development of the CNS are known to cause similar problems. Our patient’s short neck is reminiscent of the effect observed in animals exposed to PYD during early development.