[ERG diagnosis and differential diagnosis: results of examination over 6 years]

This study reviews the patient material first from the point of view of referral diagnosis. Secondly, we focus on difficulties in selective differential diagnoses.

1501 patients underwent electroretinographic (ERG) testing from 1989 to 1994, amounting to 1815 ERG recordings, including follow-up examinations. The technique applied is full-field, single flash ERG with selective stimulation of the rod- and of the cone-systems. In 3.8% (57 cases) the ERG was performed under general anesthesia in outpatients.

Tapetoretinal degenerations, toxic retinal side effects, inflammatory disease and ocular trauma represented, in this order, the major groups of referral diagnoses aside from unclear visual loss. The documentation or the exclusion of tapetoretinal degeneration represented the largest share (57%) of the application of the diagnostic procedure. 171 cases of isolated retinitis pigmentosa (RP) and 33 cases of syndromic RP were identified. Frequent and rare diagnostic entities and their differential diagnoses within this group are discussed. Inevitably, a number of diagnostic decisions remain problematic, in particular at the first examination. These diagnostic difficulties are addressed also and include the differentiation between RP sine pigmento and congenital amaurosis Leber in infants, RP with macular involvement vs. cone-rod degeneration, unilateral RP vs. postinflammatory conditions, and progressive cone dystrophy vs. achromatopsia, cone-rod degeneration or Stargardt's disease.

Frequent and meaningful indications for ERG recording and difficult diagnostic decisions arise from this review of a relatively large group of patients. A number of diagnoses can hardly, if not at all be established without ERG testing. These include retinal cause of visual loss in infants, congenital amaurosis Leber, RP sine pigmento, early stages of RP, carrier status in XL RP and in choroideremia, progressive cone dystrophy, toxic retinopathy without fundus changes, retinal involvement in uveitis with opaque media, and incomplete CSNB.