LabMed

Lambert-Eaton Myasthenic Syndrome (LEMS)

At a Glance

Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune syndrome associated with malignancies, such as small cell lung-cancer, as well as other diseases, including Sjögren's syndrome, vitiligo, and thyroid disease. The presenting symptoms are fatigue and muscle weakness, especially of the proximal leg, with weak or absent muscle reflexes. In addition, patients often complain of myalgia and dry mouth. Ptosis and diplopia are less frequent than in the related disease myasthenia gravis.

Cholinergic dysautonomia makes autonomic symptoms (e.g., dry mouth, impotence, bladder dysfunction, orthostatic hypotonia) more common than in myasthenia gravis. In one-third of cases, no tumor is detected. LEMS is caused by IgG antibodies against voltage gated calcium channels (VGCC) that lead to reduced release of acetylcholine at the neuromuscular junction.

What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?

Since neurologic symptoms can precede discovery of the tumor by several years, extensive clinical examination and laboratory testing are needed to confirm the diagnosis. (Table 1)

Table 1

Test Results Indicative of the Disorder
antibodies against VGCC (voltage gated calcium channels) electromyography 10 Hz/ decrement followed by increment of the MSAP amplitude

What Lab Results Are Absolutely Confirmatory?

The results confirmatory for LEMS are the detection of VGCC-antibodies in the blood and the increment in the repetitive stimulation EMG (the opposite finding to myasthenia gravis). In one-third of the cases, no tumor is detected.

What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?

To confirm the paraneoplastic etiology of LEMS, it is helpful to look for the paraneoplastic markers Hu- and CV-2 (CRMP)-antibodies in blood. LEMS is associated with HLA-B8 and HLA-DR3.

The endrophonium test used to diagnose myasthenia gravis is negative or only slightly positive in LEMS.

Are There Any Factors That Might Affect the Lab Results? In particular, does your patient take any medications - OTC drugs or Herbals - that might affect the lab results?

Important confounding factors are autoimmune comorbidities. The presence of acetylcholine receptor (AChR)-antibodies can give false-positive results for other autoantibodies.

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