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The Many Faces of Diabetic Neuropathy
By Jennifer A. Grillo, M.D.,
Division of Neurology/Neuromuscular Disorders
Diabetes mellitus affects millions of patients worldwide and is the most common cause of neuropathy in the Western hemisphere. A neuropathy is a lesion of the peripheral nerve that can take many forms. While incidence studies vary, approximately 7% of diabetic patients have a neuropathy at the time of diagnosis; by 25 years into the illness, 50% of patients will have a form of diabetic neuropathy.
Both Type I and Type II patients are susceptible to all manifestations of diabetic neuropathy. While the sensorimotor polyneuropathy is the most common and probably the most well known type of diabetic neuropathy, the presentation of diabetic neuropathy, treatment, and prognosis vary greatly depending on anatomical location and pathology.
The Patterns of Neuropathy
The diagnostic challenge of the neurologist is to establish the pattern of neuropathy, recognize the possible association with diabetes, and exclude other causes. Patterns of diabetic neuropathy include cranial neuropathies, such as third and sixth nerve palsies, mononeuropathies like carpal tunnel syndrome, as well as multifocal and polyneuropathies.
Multifocal Neuropathy
One of the more difficult types of diabetic neuropathy to diagnose is lumbosacral polyradiculoplexopathy, or “diabetic amyotrophy” syndrome. Pain may be the first symptom, usually in the thigh or buttock area, with notable examination findings of weakness and sensory loss in the leg. Often the pattern mimics a lumbar radiculopathy, and patients may be sent to a neurosurgeon for evaluation. The diagnosis becomes more difficult when lumbar disc disease is present concomitantly. In these cases, a detailed neurological examination and electrodiagnostic evaluation with nerve conduction studies and electromyography (NCS/EMG) can establish the correct diagnosis.
Sensorimotor Polyneuropathy
The most common neuropathy associated with diabetes is the length-dependent, symmetric, sensorimotor polyneuropathy. Although it often occurs after years of diabetes, it can be the presenting feature of new-onset Type II diabetics. Symmetric numbness in the feet in a classic “stocking” distribution is the hallmark feature. Neuropathic or burning pain may be associated with the neuropathy, but it is by no means universal. Weakness in the feet or legs may be present, but it is often mild and does not cause disability until later in the disease. While this type of neuropathy is seemingly easy to diagnose, it is important to exclude other forms of neuropathy that may appear in a similar fashion but have a completely different differential diagnosis. This is also accomplished through neurologic evaluation and electrodiagnostic studies such as EMG, quantitative sensory studies, and nerve conduction studies. Occasionally, a nerve biopsy may also be required.
Other Neuropathies
In all cases, other causes of neuropathy must be excluded. For instance, a cranial neuropathy may be caused by cerebrovascular disease such as a brainstem stroke or aneurysm. In lumbosacral polyradiculoplexopathy, a pelvic mass may cause a similar presentation. Imaging studies can exclude these possibilities. Laboratory evaluation for other metabolic, inflammatory, infectious, or neoplastic causes of neuropathy are usually required as well. Sometime the diagnosis of diabetes has not even been established, and in these cases it should be sought out.
Prognosis and Pattern of Presentation
Prognosis in diabetic neuropathy depends on the pattern of presentation. The sensorimotor polyneuropathy patient can expect to have a slowly progressive course with potential for substantial disability. While optimal blood glucose control is important to slow the progression, there is no treatment that significantly reverses the damage once the polyneuropathy is established. In other types of diabetic neuropathy, the prognosis for recovery is usually better; for instance, cranial neuropathies almost always resolve on their own. Most lumbosacral polyradiculoplexopathy cases also improve significantly with time.
Conclusion
In all these disorders, proper education and support of the patient are imperative. Treatment considerations may include pain management, physical rehabilitation, assistive devices for improved ambulation, and better blood sugar control. Although treatments for diabetic neuropathy are limited, these measures may help a diabetic neuropathy patient continue to enjoy a good quality of life.
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