| Disease Name | sporadic | | NMD Category | Disease of the Neuromuscular Junction | | Clinical Onset | adult | | Clinical Findings | This syndrome is rare and, unlike myasthenia gravis which affects mostly women, primarily affects men over the age of 40.
Strength usually is reduced in proximal muscles of the legs and arms, producing a waddling gait and difficulty elevating the arms. Some degree of eyelid ptosis or diplopia, usually mild, is found in 25% of patients. Occasionally, difficulty chewing, dysphagia, or dysarthria is present. Most patients have a dry mouth, eyes, or skin. Other symptoms may include impotence, pain in the thighs, and a pricking, tingling or creeping sensation on the skin (paresthesias) around the affected areas. In some patients, strength may improve after exercise and then weaken as activity is sustained. This is demonstrable in approximately half of all patients with ELMS. Deep tendon reflexes are reduced or absent, but frequently they can be provoked or increased by activating the appropriate muscles or by repeatedly tapping the tendon. Sensory examination is normal unless a coincident peripheral neuropathy is present, which is not uncommon in patients with underlying cancer.
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| | Diagnostic Work-up | When the ELMS diagnosis is confirmed, extensive search for an underlying malignancy is suggested. Serum or whole blood preferred for detection of antibodies to voltage-gated calcium channels (VGCC). The most effective treatment of Eaton-Lambert syndrome is the removal and effective treatment of cancer whenever diagnosed. Immunotherapy of ELMS without effective treatment of the underlying cancer usually produces little or no improvement in strength.
EMG and electron microscopy confirm the diagnosis. EMG initially shows a reduced amplitude of electrical activity in the muscle. After stimulation or exercise, the activity increases. Electron microscopy may show changes in the postsynaptic membranes and nerve cell terminals. Reflexes may be decreased and there may be muscle atrophy (loss of muscle tissue).
Progression: Symptoms usually begin insidiously. Many patients have symptoms for months or years before diagnosis is made. Progression varies with success of drug therapy and treatment of any malignancy.
| | Treatment Notes | A very important part of the diagnostic workup of Eaton-Lambert syndrome is related to the observation that almost half of the patients have or may develop an underlying cancer, most commonly a small-cell cancer of the lungs.
At the present time commercial antibody tests are not available for the Eaton-Lambert syndrome. The muscle biopsy is usually not of diagnostic help in this syndrome. In all adult patients with ELMS, imaging studies of the chest for cancer detection should be performed. A Tensilon test can be positive. A baseline muscle strength evaluation is performed. After Tensilon (edrophonium) or other short-acting neurotransmitter is given, there is a noticeable improvement of function. EMG and nerve conduction velocity tests confirm the diagnosis, with improved function as contraction is prolonged or with repetitive stimulation. AChR antibodies are found occasionally in low titers in ELMS but are more commonly associated with myasthenia gravis.
The drug dynamine is being tested as an investigational therapy.
Differential Diagnosis: Despite differences in the mechanism of disease, the symptoms of Eaton-Lambert syndrome may be similar to those of myasthenia gravis with the exception that in Eaton-Lambert the eye muscles are frequently spared and the proximal muscles are more prominently involved. Other differentials include: acute inflammatory demyelinating polyradiculoneuropathy, assessment of neuromuscular transmission, chronic inflammatory demyelinating polyradiculoneuropathy, dermatomyositis/polymyositis, inclusion body myositis, spinal muscular atrophy
| | Protein ID | 21 | | Gene Location | | | Abstract | Eaton-Lambert myasthenic syndrome (ELMS) is an autoimmune-mediated disorder of the neuromuscular junction. The patient's immune system produces antibodies to the calcium channel (voltage gate) at the nerve ending of the neuromuscular junction. With the alteration in calcium channels, appropriate levels of acetylcholine are not released and the patient develops weakness and fatigability. All patients with ELMS who have associated small-cell lung cancer have a history of long-term smoking. Only half of patients with autoimmune ELMS are long-term smokers. The cause is unknown but the disorder is usually associated with small-cell carcinoma or with autoimmune disorders.
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