Multifocal Acquired Demyelinating Sensory and Motor Neuropathy (Lewis-Sumner Syndrome)


Lewis-Sumner syndrome is a rare nerve disorder which mainly affects the arms and hands. The medical term for this syndrome is multifocal acquired demyelinating sensory and motor neuropathy (MADSAM).  Although the exact cause is unknown, it is not present at birth and not thought to be genetic so it is acquired sometime during life.

The symptoms of Lewis-Sumner are loss of feeling and tingling in the hands and arms, as well as weakness and loss of the reflexes in the arms and hands. Some patients will experience hand and arm pain as well. In some people, the syndrome also affects their legs and feet.

Symptoms are caused by an inflammation of the nerves which serve the arms and hands. This inflammation destroys or damages the fatty covering of the nerves, which is known as the myelin (say MY-lin) sheath. This destruction of the myelin sheath is known as demyelination (say DEE-my-lin-nation), which simply means to damage or remove the myelin sheath.



  • Loss of feeling in hands and arms
  • Tingling in hands and arms
  • Weakness in hands and arms
  • Loss of reflexes in hands and arms
  • Pain

Myelin insulates and protects the nerves

In normal nerves, the myelin sheath acts to insulate and protect the nerves, much like the insulation on the electrical wiring in your house or apartment. When the myelin sheath is damaged, the nerves cannot function properly and the nerve impulses slow down or even stop entirely, causing loss of sensation or inability to move the affected limb.

What is multifocal acquired demyelinating motor and sensory neuropathy?

Lewis-Sumner syndrome is also known as multifocal acquired demyelinating sensory and motor neuropathy (MADSAM) which is quite a mouthful to say  and probably just as hard to understand! But if we take it slowly and explain each term, you’ll soon understand what this means.

A neuropathy is a medical term for disease or malfunction of the nerves. So a motor neuropathy is simply a malfunction of the motor nerves, or the nerves which are responsible for movement of the limbs. A sensory neuropathy is a malfunction of the nerves which are responsible for allowing you to feel and sense things with your arms and hands. We’ve already defined the word ‘demyelinating’ which means to damage or remove the myelin sheath. As for the word ‘acquired,’ we mentioned that Lewis-Sumner syndrome is not present at birth, but acquired later in life, although the exact cause is unknown. So all that is left is the word ‘multifocal’ which means having areas of multiple focus or more than one area of the nerves is involved.

So let’s put this together in simple language. MADSAM is an acquired malfunction of the sensory and motor nerves of the upper limbs caused by damage to the nerves’ myelin sheath in multiple areas.

Diagnosis and treatment of MADSAM

Diagnosis includes a careful and thorough history and physical exam as well as a test called a nerve conduction study of the nerves of the upper limbs. This study makes use of mild electrical stimulation to let the physician see how well the nerves are working.

The treatment of Lewis-Sumner syndrome involves giving the patient intravenous injections of antibodies known as immunoglobulins and about eighty percent of patients get relief with this treatment. For the remaining patients, immunoglobulins injected under the skin or a procedure called plasma exchange (plasmapheresis) have helped many of them. About forty percent of patients for which nothing has been effective eventually get better.


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