Medicines for Lambert-Eaton myasthenic syndrome

What it is

Lambert-Eaton myasthenic syndrome (LEMS) is a rare condition in which the immune system disrupts the signals passing from the nerves to the muscles, causing muscle weakness. It is an autoimmune condition — the immune system produces antibodies that interfere with the release of the chemical (at the junction between nerve and muscle) that normally triggers the muscle to contract, so muscle activation is impaired and the muscles become weak. The characteristic feature of LEMS is muscle weakness, which typically affects the muscles closer to the centre of the body, particularly the legs (especially the thigh and hip muscles) — so people often have difficulty with activities such as walking, climbing stairs, or getting up from a chair, and the legs may feel weak and tired. A distinctive feature of LEMS is that the muscle strength may temporarily improve for a short time after a period of exercise or repeated use (unlike some other conditions where activity worsens weakness), though the weakness returns. Other features can include: weakness of other muscles (which can, in some, affect the arms, or the muscles for swallowing, speech, or, less commonly, breathing); reduced reflexes; and symptoms from the autonomic (automatic) nervous system also being affected — such as a dry mouth, and other symptoms. A very important aspect of LEMS is that, in a significant proportion of cases, it is associated with an underlying cancer — particularly a type of lung cancer (small-cell lung cancer) — where the immune reaction that causes LEMS is triggered by the cancer; the LEMS can sometimes appear before the cancer is found. Because of this, an important part of assessing LEMS is looking for an underlying cancer, so that it can be found and treated. LEMS is diagnosed by specialists (neurologists), based on the pattern of symptoms, examination, specific nerve and muscle tests, and blood tests for the relevant antibodies. LEMS is treatable: treatment includes looking for and treating any underlying cancer (which can also improve the LEMS), medicines to improve the transmission of the nerve signals and the muscle strength, and, in some cases, treatments that calm the immune system. The key messages are that LEMS is a rare autoimmune condition causing muscle weakness (especially in the legs), that it is often linked to an underlying cancer (so looking for this is important), and that it is treatable with specialist care.

How it is treated

Lambert-Eaton myasthenic syndrome is managed by specialists, with treatment including looking for and treating any underlying cancer, medicines to improve muscle strength, and, in some cases, immune-calming treatments; assessment for an associated cancer is a key part of care. Diagnosis is made by neurologists, based on the characteristic pattern of muscle weakness (particularly the legs, with the distinctive temporary improvement after exercise), examination (including reduced reflexes), specific nerve and muscle tests (which show the characteristic changes), and blood tests for the relevant antibodies. A crucial part of assessing LEMS is looking for an underlying cancer, because LEMS is associated with cancer (particularly small-cell lung cancer) in a significant proportion of cases, and the LEMS can appear before the cancer is found — so investigations to look for an underlying cancer (such as scans) are carried out, and repeated over time if none is initially found, so that any cancer can be identified and treated. Treatment of LEMS has several components. Where an underlying cancer is found, treating the cancer is important — both for the cancer itself and because treating it can improve the LEMS (as the immune reaction driving the LEMS is triggered by the cancer). For the LEMS symptoms, treatments are used to improve the muscle weakness: medicines that help improve the transmission of signals from nerves to muscles (for example, a medicine that increases the release of the chemical at the nerve-muscle junction) can improve the muscle strength and are a mainstay; and, in some cases, other medicines that improve nerve-muscle transmission are used. For LEMS that is not associated with a treatable cancer, or where more treatment is needed, treatments that calm or modify the immune system (such as immune-modulating or immunosuppressant treatments) may be used to reduce the autoimmune process, guided by specialists. Supportive care — such as physiotherapy to help with strength and mobility, and support for any swallowing, speech, or other difficulties — is also part of care. Ongoing specialist follow-up monitors the condition, the treatment, and for any underlying cancer. Because LEMS is rare and often linked to cancer, and because it is treatable, prompt assessment of unexplained muscle weakness (particularly of the legs, with the characteristic features) is important, both to treat the LEMS and to look for any associated cancer. The reassuring messages are that LEMS, although a rare autoimmune condition, is treatable — with medicines to improve muscle strength, treatment of any underlying cancer (which can also improve the LEMS), and, in some cases, immune-calming treatments — and that specialist care manages it and looks for any associated cancer; so specialist assessment (including looking for an underlying cancer), and appropriate treatment, are the keys to managing LEMS.