Marinacci communication: an electrophysiological study

Objective: Prevalence of Martin-Gruber anastomosis, an anomalous median-to-ulnar forearm communication, is well reported in literature while Marinacci communication, the reverse of Martin-Gruber with a forearm ulnar-to-median communication is under-recognized. We systematically evaluated the presence of Marinacci communication in a series of patients referred for electrophysiological studies. Methods: One hundred consecutive patients referred to the electrophysiological laboratory for various diagnoses were studied using standard techniques for motor, sensory and f wave studies. Results: Of the 100 patients (200 arms) studied, electrophysiological features of Marinacci communication were observed in 4 patients (7 arms). Median stimulation with recording over abductor pollicis brevis (APB) revealed a pseudo-conduction block over the forearm segment while on ulnar stimulation and recording over abductor digiti minimi (ADM), the amplitude of the compound muscle action potential (CMAP) obtained on proximal stimulation was higher than that obtained on distal stimulation. Ulnar stimulation at the elbow but not at the wrist revealed CMAP from APB without initial positivity. Its amplitude was 50% of the amplitude obtained on median stimulation at the wrist. Conclusions: Marinacci communication is not uncommon in the general population. A pseudo-conduction block on median stimulation and higher CMAP amplitude on proximal than distal stimulation provide valuable clues to its recognition.