N lines in a myopathy with myosin loss.

N lines can be seen by electron microscopy within the I band of skeletal muscle, but are poorly visualized in conventional preparations. We present a case of acute quadriplegic myopathy with myosin loss and prominent N lines. The only other reported cases of N lines were also seen in patients with myosin loss from diverse etiologies. Myosin loss and the subsequent detachment of titin from myosin may result in the formation of prominent N lines.