CMS Disorders

1 What are Congenital Myasthenic Syndromes?

Congenital myasthenic syndromes (CMS) are inherited conditions marked by weak skeletal muscles.

Usually ocular, bulbar or limb muscles are affected but the muscles of your heart and visceral structures are spared. The symptoms usually appear after birth or in early childhood but sometimes they may develop later in childhood.

The symptoms can be minor in mild cases whereas in severe cases, they may cause significant problems. Some symptoms are precipitated by fever, infection or excitement.

These exacerbations can cause reduced breathing (respiratory insufficiency) 

2 Symptoms

Signs and symptoms of congenital myasthenic syndromes generally develop in early childhood and rarely, they may manifest later in childhood.

Clinical features of congenital myasthenic syndromes (CMS) and myasthenia gravis (MG) are similar but immune suppressing drugs are not useful in CMS, whereas in MG they are useful.

Some of the signs and symptoms are:

  • Difficulty while feeding your child
  • Reduced ability to suck and cry
  • Choking
  • Eyelid ptosis (falling of upper eyelid)
  • Facial, bulbar, and generalized weakness
  • Inability of your lungs to inhale and exhale properly (respiratory insufficiency)
  • Temporary breathing cessation (Apnea)
  • Bluish discoloration of skin (cyanosis) due to reduced oxygen supply
  • Abnormally tired muscles that causes difficulty running or climbing stairs

When to see a doctor?

Talk to your doctor if you observe any signs or symptoms that worry you.

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3 Causes

Before we move on to determine what causes congenital myasthenic syndromes, let’s first have a look at how your muscles contract.

How does your muscle contract?

A neuromuscular junction is a site of connection between the nerves carrying motor impulses and the muscle fibers. The contraction of your skeletal muscles is facilitated by a chemical called Acetylcholine (ACh).

When you make some voluntary movements, your brain sends nerve impulses to the muscles fibers through Ach. Ach is then released from the end of the nerves which travels down the synaptic cleft (space between nerve and muscles) to the muscle fibers where it binds with specific binding sites called Ach-receptors thus causing muscle contractions.

After muscle contraction, Ach is released from its receptors into the space between muscle and nerve where it is degraded to other chemicals.

CMS occurs due to impaired signal transmission from nerve to muscles is impaired. Any genetic abnormalities causing abnormal communication of nerve with muscle fibers can lead to congenital myasthenic syndrome.

4 Making a Diagnosis

The diagnosis involves a wide range of tests to detect congenital myasthenic syndromes. Some of these tests include:

  • Medical history review
  • Blood tests to look for blood levels of antibodies against the acetylcholine receptor (AChR)
  • Electromyography or EMG test records electrical activity of your voluntary muscles while at rest and during activity
  • Genetic diagnosis: It involves identifying the mutations in the diseased gene.

5 Treatment

For treatment of a type of congenital myasthenic syndromes (CMS) called SCCMS (slow-channel CMS), the first choice is fluoxetine. But for children and teenagers quinidine is chosen because fluoxetine can cause psychiatric disturbances.

The medications used in CMS are:

  • Anticholinesterase medications, such as pyridostigmine that block the ACh-degrading enzymes.
  • 3, 4-DAP: It increases the level of ACh in neuromuscular junction. It can be either used alone or in combination with anticholinesterase.
  • Quinidine
  • Fluoxetine: It is a depression-treating medication. It may cause various psychiatric problems or may increase suicidal risk in young people. Patients taking fluoxetine should be closely observed during therapy with fluoxetine.
  • Ephedrine: It is opted for those CMS resistant to anticholinesterase.
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