Characteristics and significance of doublets on needle EMG

Voluntary doublets are electrophysiological phenomena thought to be associated with metabolic derangements or neuromuscular conditions.

We prospectively studied 232 consecutive patients examined by a single examiner during routine electromyography (EMG) to determine the frequency of doublets in individual patients, specific muscles, neuromuscular conditions, electrolyte levels, and doublet characteristics.

Of 232 patients, 25 (10.7%) exhibited doublets. The mean age was 59 (52% men). Only 32 of 1,303 (2.5%) muscles exhibited doublets. Lower extremity and paraspinal groups represented 91% of muscles with doublets. Doublet frequency grouped by EMG diagnoses was: ALS (3 of 11; 27.1%), myopathy (3 of 10; 30.0%), axonal polyneuropathy (7 of 29; 24.1%), and no disease (7 of 109; 6.4%). There were no differences in serum electrolytes between doublet and matched subjects.

Doublets occur in approximately 10% of patients, more commonly in lower extremity and paraspinal muscles, and are not correlated with a specific metabolic abnormality or neuromuscular condition. Muscle Nerve 55: 598-600, 2017.