Abnormal Electromyographic Findings in a Patient with Negative Scotopic Electroretinogram and Normal Dark Adaptation

Abstract

Purpose: To present ocular and electromyographic findings in a patient with negative scotopic electroretinogram (ERG), reduced ON response, and normal dark adaptation. Patient: A 21-year-old Japanese female patient who complained of blurred vision. Her corrected visual acuity was 1.5 in each eye. Both fundi were normal. Dark adaptometry showed a normal pattern. Methods: The patient underwent ERG, contrast sensitivity testing, and electromyography (EMG). Results: The rod b-wave was reduced and delayed in the scotopic ERG. Scotopic bright flash response showed negative configuration. In the photopic responses to long flash, b-wave (ON response) was significantly reduced, while d-wave (OFF response) was within the normal range. The contrast sensitivity measurement showed high-frequency loss. Although she did not show muscle atrophy, weakness, or elevation of serum creatine kinase, the existence of myopathy was suggested by the EMG results. Conclusions: Dysfunctions of both rod and cone ON-bipolar cells were evident in the ERG findings. All ophthalmological results, except contrast sensitivity, were consistent with previous reports of diseases with an abnormal dystrophin gene condition: dystrophinopathy and its female carriers. The combination of negative ERG, reduced ON response, and normal dark adaptation might be a predictive indicator for muscle diseases such as dystrophinopathy and its female carriers.

KEYWORDS:

• Dark adaptation
• myopathy
• negative scotopic electroretinogram (ERG)
• reduced ON response
• dystrophin