Axonopathies are usually distal; they may be symmetric or asymmetric.
Symmetric axonopathies result most often from toxic-metabolic disorders. Common causes include the following
• Diabetes mellitus: in diabetic individuals, blood sugar would be too high. With time, this can harm the covering on your nerves or the blood vessels that bring oxygen to your nerves, and they will start to “malfunction”. This damage is called diabetic neuropathy. More than half of people with diabetes get it. Symptoms may include
o Numbness in your hands, legs, or feet
o Shooting pains, burning, or tingling
• Chronic renal insufficiency (due to chronic kidney disease; with elevated creatinine in the blood and abnormal electrolytes) can induce damage in the nerves
• Adverse effects of chemotherapy drugs (eg, vinca alkaloids)
• Guillain Barré syndrome: a disorder in which the body's immune system attacks part of the peripheral nervous system. Weakness, tingling, and abnormal sensations that starts in the legs and progresses quickly upwards are typical. It usually occurs after a viral illness.
Less common metabolic causes include hypothyroidism (poor thyroid gland function), porphyria (porphyrias are a group of genetic disorders caused by problems with how your body synthesizes a substance called heme; heme is found especially in the red blood cells and bone marrow, where it carries oxygen), sarcoidosis (a disease that causes inflammation, usually in the lungs, skin, or lymph nodes. It starts as tiny, grain-like lumps, called granulomas. It can affect any organ in your body), and amyloidosis (occurs when abnormal proteins called amyloids accumulate and form deposits, which can reside in organs such as the kidney and heart. This can cause the organs to become stiff and unable to function properly).
Other causes include certain infections (eg, Lyme disease; uncommon in our part of the world, more commonly seen in America), drugs (eg, nitrous oxide), and exposure to certain chemicals (eg, Agent Orange, n-hexane) or heavy metals (eg, lead, arsenic, mercury).
When the axon (please refer to my previous answer for the definition of axon) is not functioning as it should, there will be neuropathy distally (at the ends of the arms and/or legs) which is distributed in a symmetric fashion. A “stocking-glove distribution” is characteristic, with abnormal sensation on the hands and feet, as if you’re wearing gloves and stocking; it evenly affects the legs before the arms and progresses symmetrically from distal (ends) to proximal areas.
If your symptoms are asymmetric, tests for hypercoagulable states (excessive blood clotting which leads to blood vessel blockage hence no oxygen reaches the nerves) and infectious causes, or autoimmune vasculitis (when your own immune system attacks your blood vessles), particularly if suggested by clinical findings, should be done; the minimum is ESR, serum protein electrophoresis (A method for determining protein homeostasis in the body), and measurement of rheumatoid factor, antinuclear antibodies, and serum creatine kinase, an enzyme found in the nerves and muscles and is responsible for generating energy in the form of ATP, a high-energy molecule used by the body). CK may be elevated when rapid onset of disease results in muscle injury. Coagulation studies should be done only in the setting of a personal or family history of a hypercoagulable state. Tests for sarcoidosis, hepatitis C, or granulomatosis with polyangiitis (formerly known as Wegener granulomatosis) should be done only if symptoms and signs suggest one of these disorders
F Guillain Barré is suspected, a spinal tap (to test the cerebro-spinal fluid, the fluid that circulates around the brain and spinal cord) is done to look for certain evidence of the disease: high protein but low normal blood cells. Additionally, an electromyogram (EMG) and nerve conduction studies are done to check if muscles and nerves are sending messages correctly.
If no cause is identified, nerve and muscle biopsy should be done. Nerve biopsies are useful in symmetric and asymmetric polyneuropathies but are particularly useful in asymmetric axonopathies.
If initial tests do not identify the cause of distal symmetric axonopathies, a 24-h urine collection is tested for heavy metals, and urine protein electrophoresis is done if chronic heavy metal poisoning is suspected.
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