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Wednesday, January 07, 2009

Dying Back Neuropathy is due to all except Gullain Barre Syndrome

Question 77
Dying Back Neuropathy is due to all except
a.       Gullain Barre Syndrome
b.      Arsenic
c.       DM
d.      Porphyria
Answer
a. Gullain Barre Syndrome
Reference
Nelson 15th Edition Chapter 565,  Table 76–2
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Discussion
Although peripheral neuropathy has multiple etiologies, the nerve has a limited number of ways to respond to injury. The damage can occur at the level of the axon (i.e., axonopathy). A disruption of the axons (e.g., trauma) results in degeneration of the axon and the myelin sheath distal to the site of the injury (i.e., Wallerian degeneration). In most toxic and metabolic injuries, the most distal portion of the axons degenerates, with concomitant breakdown of the myelin sheath (known as "dying-back," or length-dependent, neuropathy).
Explanation
a.       Gullain Barre Syndrome is a postinfectious polyneuropathy that causes demyelination in mainly motor but sometimes also sensory nerves. It is not a predominant distal neuropathy
b.      Many chemicals (organophosphates), toxins, and drugs are capable of causing peripheral neuropathy. Heavy metals are well-known neurotoxins. Lead poisoning, especially if chronic, causes mainly a motor neuropathy involving selective large nerves, such as the common peroneal, radial, or median nerves, a condition known as mononeuritis multiplex. Arsenic produces painful burning paresthesias as well as motor polyneuropathy.
c.       Polyneuropathy is the commonest type of diabetic neuropathy. The feet get involved first. When the neuropathy progresses then symptoms ascend from the toes to foot and gradually further to the knees. Later the hands may get involved. The symptoms of neuropathy are always worse at night. The commonest symptom is numbness.
d.      Porphyria  (AIP) presents with Neurologic manifestations like nausea, vomiting, abdominal pain, diarrhea, constipation, ileus, dysuria muscle               hypotonia, respiratory failure, sensory neuropathy, seizures
Comments
Ä     Antimetabolic drugs, especially vincristine, produce polyneuropathies as complications of chemotherapy for neoplasms.
Tips
Ä     Chronic uremia is associated with toxic neuropathy and myopathy. The neuropathy is due to excessive levels of circulating parathormone. Reduction in serum parathyroid hormone is accompanied by clinical improvement and a return to normal of nerve conduction velocity.

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