Peripheral (limb) myokymic discharges in motor neuron disease

We present the case of a 28-year-old gentleman who presented with weakness and wasting in the right arm. He complained about painful cramps in his left leg but there were no sensory, visual or swallowing problems. Neurological examination was significant for asymmetric weakness of both upper and lower limbs and deep tendon reflexes were asymmetrically brisk. Initial laboratory investigations, MRI brain and MRI spine were normal. Electromyography revealed active denervation and chronic neurogenic motor unit action potential. Myokymic discharges were noted in the left deltoid muscle.