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Neuro Muscular Disorders

• nerve
• neuromuscular junction, and
• muscle fibers

• Neuropathy
• Diabetic neuropathy
• Myopathy
• ALS (Lou Gehrig's Disease)
• Myasthenia gravis
• Guillain Barre syndrome

The problem.

Neuromuscular diseases constitute one of the major causes of ongoing disability in childhood. While some of these disorders are treatable, for many children there is currently no cure.

Children with neuromuscular disorders have significant and worsening disabilities; many children are unable to walk and, in severe cases, the weakness impairs the muscles of breathing resulting in death at an early age.

Most neuromuscular disorders of childhood are genetic and more than one person in a family may be affected. For example, the muscular dystrophies are a group of hereditary muscle diseases, which can result in severe and often progressive muscle weakness. Inherited nerve disorders, known as peripheral neuropathies can affect the transfer of messages within the body. When the muscle loses its nerve supply it "wastes away" resulting in progressive loss of motor function.

Neuropathy can be divided into five categories based upon clinical localization. (1)  Mononeuropathies are usually traumatic or due to entrapments, such as the carpal tunnel syndrome. You should be familiar with median, ulnar, radial, peroneal and lateral femoral cutaneous nerve syndromes. Multiple mononeuropathy (mononeuritis multiplex) should first suggest systemic vasculitis, requiring urgent evaluation for diagnosis and treatment to avoid serious disability or death. (2)  Polyneuropathy affects the longest nerves first, with symptoms therefore beginning in the feet. Signs are atrophy of intrinsic foot muscles, reduced or absent ankle jerk, and distal (A S tocking @ ) sensory loss. Etiologies are usually metabolic or toxic. (3)  Radiculopathy, with pain radiating from the neck or low back to one extremity, usually has subtle if any findings on neurological exam. Herniated disk, spondylosis and Herpes zoster are the common causes. (4)  Polyradiculoneuropathies are usually bilateral, but differ from polyneuropathies in that symptoms and signs are as likely to be proximal as distal. The differential diagnosis includes Guillain-Barré syndrome when acute or subacute, and when chronic, CIDP (chronic inflammatory demyelinating polyradiculoneuropathy) and a variety of neuropathies associated with paraproteinemias. (5) Finally, plexopathies affect usually one limb, are painful, and are associated with considerable neurological deficit. Trauma, neoplasm, and radiation are in the differential diagnosis, but when pain and weakness occur subacutely (days to weeks) without trauma or tumor, the diagnosis is most commonly idiopathic when the brachial plexus is involved, and diabetic amyotrophy when the lumbosacral plexus is involved.

Disorders of Neuromuscular Transmission: Myasthenia gravis, an autoimmune disorder with antibodies directed against the acetyl choline receptor, typically presents with ocular (ptosis, diplopia) and bulbar (dysarthria, dysphagia, neck weakness) symptoms and signs and proximal weakness, with preserved tendon reflexes and no sensory disturbances. The Tensilon test and antibodies to acetyl choline receptor are helpful diagnostically. Treatment with anticholinesterases, thymectomy, and immuno­suppressants of various kinds is usually effective. The Lambert-Eaton myasthenic syndrome results from antibodies to calcium channels in the nerve endings, reducing the release of acetyl choline. Proximal weakness, autonomic disturbances, and decreased reflexes are common, and electrophysiological studies are often diagnostic. In many patients there is an associated neoplasm (most often small cell cancer of the lung).

Disorders of Muscle usually present with symmetrical proximal weakness without sensory loss. Tendon reflexes may be normal or reduced. There are many inherited disorders of muscle that for the most part are the purview of specialists. You should be aware of the muscular dystrophies, particularly myotonic dystrophy, which is a multisystem disease that often presents with symptoms other than weakness. Acquired myopathies are often treatable. All patients should get thyroid functions studies. Cushing = s syndrome and other endocrinopathies should be considered. Inflammatory myopathies include two autoimmune disorders, polymyositis and dermatomyositis, that usually respond to appropriate treatment. Adults with dermatomyositis have a high incidence of cancer. Finally, medication-induced myopathy and myopathy associated with HIV infection should be considered.