Continuous infusion therapy after deep brain stimulation in Parkinson's disease: indications, outcomes, and patient selection.

Patients with Parkinson's disease now live for decades after deep brain stimulation, and many develop recurrent symptoms while the stimulator still functions. A continuous infusion is sometimes added, but the circumstances justifying it are undefined, and the two modalities are still viewed as competing rather than complementary. This review examines the addition of the four infusion therapies after stimulation. A search of three databases identified fifteen reports, almost all small and retrospective. They report 118 patients and 119 infusion courses: 68 with intestinal levodopa gel, 23 with apomorphine, 28 with foslevodopa/foscarbidopa, and none with entacapone. Off time fell in every study that measured it, though fewer than half did. The on-state motor examination improved significantly only in the largest series to test it. In a post hoc trial subgroup, off time improved similarly with and without previous stimulation, while activities of daily living and speech improved significantly less in those with prior stimulation. Severe adverse events were more frequent after prior stimulation. The combination is uncommon: 1% to 2% of patients in larger cohorts, under 0.1% in a national apomorphine cohort. Stimulation parameters are reported or unchanged in only 10 of the 118 patients, and primary failure cannot be separated from secondary failure in 29. We propose a structured assessment separating correctable device problems, recurrent dopaminergic symptoms, stimulation-induced effects and levodopa-resistant progression. Infusion therapy may help recurrent levodopa-responsive complications after stimulation has been re-evaluated and optimized. Its use in late axial or cognitive decline is untested rather than disproven.