Diagnostic value of the electromyography of the extraocular muscles

The electromyography (EMG) of the extraocular muscles (EOM) represents a special form of electrophysiological investigation techniques which can be offered only in a few centers with special ophthalmologic and neurophysiologic expertise due to its special characteristics. The diagnostic value of the EOM-EMG is especially apparent in neuromuscular diseases which occur with predominantly ocular manifestation.

Needle EMG examinations of EOM were performed in a cohort of 206 patients with a variety of relevant disorders mainly with a neurological focus. The results of these EMG examinations were assessed retrospectively. After local anaesthesia of the sclera and using a lid retractor to keep the eye open the EOM were identified visually by an experienced ophthalmologist and the needle was inserted. The EMG activity was registered in resting position, in mild volitional, and at maximum activation. The assessment was performed visually on a monitor by an experienced neurophysiologist.

In the group of neuromuscular (myopathic) diseases, the results of the EOM-EMG were compatible with the clinical diagnosis in 54 of 65 patients (83%) and in 69 of 85 patients (81%) in the group with peripheral lesions. In a "Varia" group (n=56) no diagnosis could be established despite all further investigations in 31 patients. In the remaining patients, the EOM-EMG result was compatible with the diagnosis in 22 of 25 patients (88%). Subgroup analysis revealed that particularly in myositis (30 of 33 findings in 32 patients, one patient was examined twice; 91%), muscle dystrophy (7 of 8 patients; 88%) and in isolated nerve lesions (64 of 79 patients; 81%) the diagnosis could be positively proven by the EOM-EMG. Clinically relevant complications were not observed.

The EOM-EMG is safe and has a high diagnostic value especially in diseases such as myositis, muscular dystrophy and isolated peripheral nerve lesions.

With better knowledge of the diagnostic value of the EOM-EMG in various diseases, less relevant diagnostic investigations can be avoided in the future. Moreover, a higher degree of trust in the method should facilitate the decision to perform this special diagnostic method.