DIAGNOSING AXONAL SENSORIMOTOR POLYNEUROPATHY IN THE ELDERLY

Lumbosacral polyradiculopathy from lumbar canal stenosis is a common cause of nerve damage in the elderly. The clinical presentation can be similar to axonal sensorimotor polyneuropathy, with sensory and motor changes in a distal more than proximal distribution.  In addition, absent ankle deep tendon reflexes and mild loss of vibratory sensation at the distal lower extremity can be normal findings in the healthy elderly population.

A number of factors contribute to the difficulty in differentiating lumbosacral polyradiculopathy from axonal sensorimotor polyneuropathy in the elderly.  Symptoms of lumbar canal stenosis, such as gait difficulty,may be insidiously progressive and nonspecific.  Confounding factors in the elderly limit the value of electrodiagnostic testing, including the physiologic loss of sensory responses and the presence of nonspecific changes on needle EMG at the distal lower extremity that prevent a reliable diagnosis of polyneuropathy and a distinction from polyradiculopathy.

Nerve conduction studies of the arm can be useful in this setting, as sensory responses at the hand are preserved at all ages, unless the patient has a generalized polyneuropathy.  EMG of proximal leg muscles is helpful to assess for a radicular pattern of involvement. Lumbosacral MRI is useful when a clinical suspicion of intraspinal disease exists.