Observations on severe ulnar neuropathy in diabetes.

We describe the clinical and neurophysiologic findings in a group of diabetic patients with a severe ulnar neuropathy. All patients attending a large inner-city diabetes center were prospectively screening for hand wasting and weakness due to ulnar nerve disease. Twenty diabetic patients fulfilling the clinical criteria underwent nerve conduction studies and electromyography. All but one patient with a motor ulnar neuropathy had systemic complications, mostly severe: ten were amputees, four had had a renal transplant, and two were blind. The onset of hand weakness was sudden in five. All patients had a classical "ulnar hand" (bilateral in five) but forearm muscles were little affected. Sensory loss was prominent in only one-half. Nerve conduction studies showed markedly reduced ulnar motor responses (mean, 1.2 mV versus 7.4 mV in controls) and ulnar/median motor ratios. Motor conduction was disproportionately slowed across the elbows, with or without conduction block, in only eight of 34 affected ulnar nerves. Five of these patients had a habit of leaning on their elbows and/or a Tinel's sign. Median sensory action potentials (SAPs) were recordable in 12 patients but ulnar SAPs were absent in 30 of 34 affected nerves. Electromyography revealed advanced denervation of ulnar supplied hand muscles. We conclude that motor ulnar neuropathy is not uncommon in patients with diabetes of long standing, especially in those with severe systemic complications. Nerve entrapment at the elbows occurs in some, but in many the lesion is axonal, and damage may occur through ischemia.