neurologic disorders
Polyneuropathy
Symptoms and Signs of Polyneuropathy
Symptoms of polyneuropathy may appear suddenly or develop slowly and become chronic depending on the cause. Because pathophysiology and symptoms are related, polyneuropathies are often classified by area of dysfunction: Myelin Vasa nervorum Axon Polyneuropathies may be acquired or Hereditary Neuropathies . Myelin dysfunction (demyelinating) polyneuropathies most often result from a parainfectious immune response triggered by encapsulated bacteria (eg, Campylobacter and Related Infections sp), viruses (eg, enteric or In acute cases (eg, in Guillain-Barré Syndrome (GBS) ), rapidly progressive weakness and respiratory failure may develop. In Myelin dysfunction usually results in large-fiber sensory disturbances (paresthesias), significant muscle weakness greater than expected for degree of atrophy, and greatly diminished reflexes. Trunk musculature and cranial nerves may be involved. Demyelination typically occurs along the entire length of a nerve, causing proximal and distal symptoms. There may be side-to-side asymmetries, and the upper body may be affected before the lower body, or vice versa. Muscle bulk and tone are relatively preserved. Chronic arteriosclerotic ischemia, vasculitis, infections, and hypercoagulable states can compromise the vascular supply to nerves, causing nerve infarction. Usually, small-fiber sensory and motor dysfunction occurs first. Patients typically have painful, often burning sensory disturbances. Pain and temperature sensation are deficient. Vasa nervorum involvement (eg, caused by vasculitis or infections) can begin as multiple mononeuropathies, which, when many nerves are affected bilaterally, can look like polyneuropathy. Abnormalities tend to be asymmetric early in the disorder and rarely affect the proximal one third of the limb or trunk muscles. Cranial nerve involvement is rare, except in diabetes, which commonly affects the 3rd cranial (oculomotor) nerve and, slightly less commonly, the 6th cranial (abducens) nerve. Later, if nerve lesions coalesce, symptoms and signs may appear symmetric. Dysautonomia and skin changes (eg, atrophic, shiny skin) sometimes occur. Muscle weakness tends to be proportional to atrophy, and reflexes are rarely lost completely. Axonopathies tend to be distal; they may be symmetric or asymmetric. Symmetric axonopathies result most often from toxic-metabolic disorders. Common causes include the following: Diabetes Mellitus (DM) None Chronic Kidney Disease None Adverse effects of chemotherapy drugs (eg, vinca alkaloids) Axonopathy may result from nutritional deficiencies (most commonly, of Thiamin Deficiency , In a Paraneoplastic syndromes associated with small-cell lung cancer, loss of dorsal root ganglia and their sensory axons results in subacute sensory neuropathy. Primary axon dysfunction may begin with symptoms of large- or small-fiber dysfunction or both. Usually, the resulting neuropathy has a distal symmetric, stocking-glove distribution; it evenly affects the lower extremities before the upper extremities and progresses symmetrically from distal to proximal areas. Asymmetric axonopathy can result from parainfectious or vascular disorders. 