Lambert–Eaton myasthenic syndrome (LEMS) is a rare autoimmune disorder characterized by muscle weakness of the limbs.

[4] The diagnosis is usually confirmed with electromyography and blood tests; these also distinguish it from myasthenia gravis, a related autoimmune neuromuscular disease.

Other treatments often used are steroids, azathioprine, which suppress the immune system, intravenous immunoglobulin, which outcompetes autoreactive antibody for Fc receptors, and pyridostigmine and 3,4-diaminopyridine, which enhance the neuromuscular transmission.

Some may have double vision, drooping of the eyelids and difficulty swallowing,[4] but generally only together with leg weakness; this too distinguishes LEMS from myasthenia gravis, in which eye signs are much more common.

This may be experienced as a dry mouth, constipation, blurred vision, impaired sweating, and orthostatic hypotension (falls in blood pressure on standing, potentially leading to blackouts).

[4] On neurological examination, the weakness demonstrated with normal testing of power is often less severe than would be expected on the basis of the symptoms.

[3] LEMS may also be associated with endocrine diseases, such as hypothyroidism (an underactive thyroid gland) or diabetes mellitus type 1.

Repeated stimuli over a period of about 10 seconds eventually lead to sufficient delivery of calcium, and an increase in muscle contraction to normal levels, which can be demonstrated using an electrodiagnostic medicine study called needle electromyography by increasing amplitude of repeated compound muscle action potentials.

[3][6] The diagnosis is usually made with nerve conduction study (NCS) and electromyography (EMG), which is one of the standard tests in the investigation of otherwise unexplained muscle weakness.

NCS investigation in LEMS primarily involves evaluation of compound motor action potentials (CMAPs) of effected muscles and sometimes EMG single-fiber examination can be used.

If repeated impulses are administered (2 per second or 2 Hz), it is normal for CMAP amplitudes to become smaller as the acetylcholine in the motor end plate is depleted.

[4][3] On single-fiber examination, features may include increased jitter (seen in other diseases of neuromuscular transmission) and blocking.

[4] Once LEMS is diagnosed, investigations such as a CT scan of the chest are usually performed to identify any possible underlying lung tumors.

Prednisolone (a glucocorticoid or steroid) suppresses the immune response, and the steroid-sparing agent azathioprine may replace it once therapeutic effect has been achieved.

Again, plasma exchange is less effective than in other related conditions such as myasthenia gravis, and additional immunosuppressive medication is often needed.

[4] Three other treatment modalities also aim at improving LEMS symptoms, namely pyridostigmine, 3,4-diaminopyridine (amifampridine), and guanidine.

[4][3] Pyridostigmine decreases the degradation of acetylcholine after release into the synaptic cleft, and thereby improves muscle contraction.

[10] Anderson and colleagues from St Thomas' Hospital, London, were the first to mention a case with possible clinical findings of LEMS in 1953,[11] but Edward H. Lambert, Lee Eaton, and E.D.

[14] Studies in the 1980s confirmed the autoimmune nature,[6] and research in the 1990s demonstrated the link with antibodies against P/Q-type voltage-gated calcium channels.