Confusion and ataxia in a patient with bipolar

Marion, a 65-year-old woman, is brought to her GP by her sister, Rhonda.
When Rhonda went to Marion’s home that morning to check on her after not hearing from her for a few days, she found Marion in bed, apparently confused.
She appeared off-balance and required Rhonda’s help to mobilise.
Marion lives alone. She has a history of bipolar affective disorder, treated with lithium, and recently diagnosed hypertension, treated with perindopril.