Hydroxychloroquine Retinopathy - False Positive Ancillary Testing

This patient was a man of height 6 feet, weight 205 pounds who began to take hydroxychloroquine 400 mg/d in March 2011. His baseline examination for the purposes of subsequent screening for toxicity occurred in May 2011. The 10-2 visual field test with the red test light showed paracentral scotomata OU although there was no macular abnormality on funduscopy and he was on a dose of hydroxychloroquine within the acknowledged range for low risk of retinopathy. The mf ERG was abnormal as well, with low P wave amplitudes for ring 2 in the right eye and rings 1-3 in the left eye although the R1/R2 ratio was normal bilaterally. This case illustrates that all ancillary tests have a certain percentage of cases that are falsely positive. The patient clearly does not have hydroxychloroquine retinopathy, yet the screening tests suggest such. One must integrate the results of ancillary testing with the clinical picture. In this case, the patient is on acknowledged safe dosing for 2 months, a duration never before associated with retinopathy. He was followed at 6 month intervals expecting the 10-2 VF to improve with greater familiarity with the testing protocol, and interpreting his mfERG as simply reflecting the fact that 5% of persons will have lower amplitudes than the lower bound of normal accepted by convention.