Symptoms Congenital myasthenic syndrome (CMS)

While various symptoms may need further investigation, they can vary greatly from person to person and not all symptoms will be found or experienced in the same way.

The following symptoms may be noticed in someone with Congenital myasthenic syndrome (CMS):

  • in the womb: decreased movement and too much amniotic fluid (polyhydramnios)
  • from birth: stiff joints (arthrogryposis), reduced movements, a weak suck and cry, difficulty feeding, swallowing and possibly episodic breathing difficulties
  • in childhood: may start walking late, become tired with exercise, only able to walk short distances, unable to hold their arms above the head for long, and have difficulty climbing stairs. They may also have difficulty chewing food, scoliosis (curvature of the spine), a waddling gait and a tendency to fall easily. Sometimes there are distinctive facial features such as a prominent lower jaw, high arched palate and crowded teeth (maloclusion), droopy eyes when tired, reduced eye movement with occasional double vision and unclear or nasal speech. Children with CMS may also get frequent chest infections and need hospital treatment
  • in adulthood: may have similar problems to those of children but these will be noticed at a later age. They are often poor at sport, easily fatigued especially on climbing stairs and have weakened ability to move their fingers and wrists.

Symptoms can vary greatly from person to person and not all will be present or experienced in the same way. Fatigue is a common characteristic.

Many other conditions that affect muscle, nerve and brain function can cause similar symptoms to the above.

How does CMS progress?

It is important to get a correct diagnosis to be able to predict the long-term outcome. If diagnosed early, CMS can be treated and prevented to some extent with medication. Almost all children with CMS will be able to walk independently and it does not affect intellect in any way. Some CMS is so mild that it is only diagnosed in late childhood, adolescence or even adulthood. Supportive treatment is offered in all cases.

Breathing support, help with feeding, monitoring of lung function, physiotherapy and speech and language therapy may be needed. Most people with CMS find their muscle strength improves with time and the need for medication reduces. In some rare cases, there is no treatment that helps. Some will need life-long medication to maintain muscle strength. In some instances, body strength may improve with treatment, but eyelid droop and eye movements do not.