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For people with Down syndrome, family members, caregivers and professionals.

Startle Reflex and Myoclonus

February 2018 | Brian Chicoine, MD - Medical Director, Adult Down Syndrome Center

We were asked a question about increased “startle reflex” in a 30-year-old.

Please note: The information below is for educational purposes only and is not intended to serve as a substitute for a medical, psychiatric, mental health, or behavioral evaluation, diagnosis, or treatment plan by a qualified professional.

The Moro reflex, also called startle reflex, is a reflex a newborn baby exhibits that normally disappears in the first several months of life. The infant makes sudden body movements with a change in position.

Increased startle that develops later in childhood or in adulthood is different. It may be myoclonus. Myoclonus, as described in UpToDate, is “a clinical sign that is characterized by brief, shock-like, involuntary movements caused by muscular contractions or inhibitions…Patients will usually describe myoclonus as consisting of ‘jerks,’ ‘shakes,’ or ‘spasms.’” (1)

Physiological myoclonus is a normal occurrence in healthy people. A sudden jerk during transition from awake to sleep, during sleep, or as a response to anxiety are examples. It might also be referred to as an exaggerated startle.

Myoclonus can have several other causes including, but not limited to:

  • Genetic causes
  • Neurological causes, including seizures
  • Medication side effects
  • Withdrawal from medications
  • Metabolic disorders (e.g. kidney disease, hyperthyroidism)
  • Infectious causes

In our experience, some of the more common causes to consider for people with Down syndrome include:

  • Exaggerated physiological myoclonus associated with anxiety
  • Medication side effects
  • A form of seizures (particularly in older individuals who have developed Alzheimer’s disease)
  • Atlanto-axial instability or any cervical subluxation with myelopathy (spinal cord injury)
  • Hyperthyroidism (overactive thyroid)
  • Electrolyte disturbances due to a variety of illnesses and condition
  • Excess caffeine consumption

A good assessment by the primary health care provider will often find the cause. Some individuals will benefit from a consult with a neurologist. Other consults as needed may be indicated. Treatment will depend on the cause. If the myoclonus is mild and no concerning cause is found, monitoring without treatment is appropriate for some individuals.

 

References

1. Caviness, JN. Classification and evaluation of myoclonus. In: Hurtig HI, ed. UpToDate. Waltham, Mass.: UpToDate; 2019. www.uptodate.com. Accessed February 18, 2019. 

Please note: The information on this site is for educational purposes only and is not intended to serve as a substitute for a medical, psychiatric, mental health, or behavioral evaluation, diagnosis, or treatment plan by a qualified professional. We recommend you review the educational material with your health providers regarding the specifics of your health care needs.

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