Peripheral Nerve Problems for the Physician Assistant Exam
Many disorders can affect the integrity of the peripheral nerves. For the Physician Assistant Exam (PANCE), make sure you are familiar with peripheral neuropathy and complex regional pain syndrome (CRPS).
One of the best examples of a peripheral neuropathy is diabetic neuropathy, a polyneuropathy that affects the hands and feet in a glove-stocking distribution. A peripheral neuropathy sometimes affects just one nerve (a mononeuropathy), as in carpal tunnel syndrome, which affects the median nerve. A neuropathy can also affect multiple nerves, as in vasculitis or a connective tissue disease like systemic lupus erythematosus.
Peripheral neuropathies can be debilitating. Common presenting symptoms include sensory symptoms (including numbness, tingling, and paresthesias) and motor symptoms (including weakness).
The treatment of the peripheral neuropathy depends on the underlying cause. Look at the following examples:
The treatment for diabetic neuropathy is prevention with intensive blood glucose control. Medications such as gabapentin (Neurontin), duloxetine (Cymbalta), and the tricyclic antidepressants can help with the pain.
The treatment for peripheral neuropathy secondary to B12 and folic acid deficiency is replacement. B12 deficiency can cause subacute combined degeneration, which is a loss of vibration and proprioception.
Amyloidosis can cause a peripheral polyneuropathy, an autonomic neuropathy, or a restrictive cardiomyopathy. The treatment is chemotherapy.
Exposure to heavy metals, including lead, can cause a peripheral neuropathy. The treatment for this involves intravenous chelation.
HIV can cause many kinds of neuropathy. The treatment includes the use of some of the medications in addition to treatment directed against the HIV.
Another example of a peripheral neuropathy is an autonomic neuropathy, which involves a blunting of the sympathetic nervous system. The most common cause of this is diabetes mellitus. With an autonomic neuropathy, there’s usually orthostatic hypotension but without a corresponding increase in heart rate.
Complex regional pain syndrome
Complex regional pain syndrome, formerly known as reflex sympathetic dystrophy, can be a very debilitating condition. An extremity is often in extreme pain after some inciting event, usually a significant trauma. The thought is that after inciting event, the person has an exaggerated inflammatory response, which worsens the pain. Another thought is that the person has a heightened sympathetic tone. The nerve is affected as a result of the injury.
The affected extremity is red, warm, and painful to touch. Complex regional pain syndrome involves nerve damage, which can affect the muscles and even the bone. On a radiograph or bone scan, the bone can have the look of osteoporosis.
Here are key points about complex regional pain syndrome:
The pain is out of proportion to the injury that caused it (allodynia).
The affected person’s extremity is very sensitive (hyperalgesia).
The pain and paresthesias can worsen over weeks to months.
The person may have a low blood flow and labile temperatures over the affected limb.
The muscles of that extremity can atrophy.
Treatment is based on trying to help with pain, and that may decrease sympathetic tone or even stimulate the nerves. If this condition is diagnosed too late, it may not be reversible.