Objective To evaluate the long-term effectiveness of dietary therapy with regular dietetic reinforcement for adult Refsum disease.

Methods Retrospective case note analysis of records of plasma phytanic acid and hospital admission of 13 patients with adult Refsum disease who attended the specialist centre and repeatedly received dietary instruction for a minimum of 10 years.

Results Patients undergoing review had attended for 11–28 years totalling 237 years. Median baseline phytanic acid concentrations at presentation were 1631 (370–2911) μmol/l and declined by 89±11% to 85 (10–1325) μmol/l. Levels of phytanic acid were completely normalised (<30 μmol/l) in 30%; partially normalised (30–300 μmol/l) in 50% and remained >300 pmol/l in 15%. The time required for phytanic acid levels to halve was 44.2±15.9 months in patients compliant with diet. No patient required admission or plasmapheresis/apheresis during this period for acute neuro-ophthalmological complications despite occasional spikes in phytanic acid levels attributable to intercurrent illness, surgery, sudden weight loss or psychological illness.

Interpretation Dietary modification with regular reinforcement in Adult Refsum Disease can significantly reduce phytanic acid levels with time.