Final answer:
The most likely cause of new-onset seizures in a cerebral palsy patient receiving baclofen via a gastrostomy tube who has been stable on the medication for three months is missed doses of baclofen, leading to withdrawal symptoms. Therefore, the correct option is a.
Step-by-step explanation:
A patient with cerebral palsy who is receiving baclofen via a gastrostomy tube and presents with new-onset seizures may be suspected of having missed doses of baclofen. Baclofen is a medication used to reduce muscle spasticity, and abrupt discontinuation or missed doses can lead to withdrawal symptoms, one of which can be seizures. While baclofen toxicity or a common adverse effect of the medication could potentially cause seizures, these are less likely if the drug has been administered consistently without issue for three months. Idiopathic causes related to the disease process are always a consideration, but given the patient's stable medication regimen and the acute onset of seizures, missed doses of baclofen are the most likely cause.