Stereotypic movement disorder

# Overview
Stereotypic movement disorder is a disorder of childhood involving repetitive, nonfunctional motor behavior (e.g., hand waving or head banging), that markedly interferes with normal activities or results in bodily injury, and persists for four weeks or longer.  The behavior must not be due to the direct effects of a substance or another medical condition.  In cases when mental retardation is present, the stereotypic or self-injurious behavior must be of sufficient severity to become the focus of treatment.  The behavior is not better explained as a compulsion (e.g.; OCD), a tic, a stereotypy as part of a pervasive developmental disorder, or hair pulling (trichotillomania).  Former versions of the DSM (Diagnostic Manual and Statistical Manual of Mental Disorders) used the term Stereotypy/Habit Disorder to designate repetitive habit behaviors that caused impairment to the child.  When stereotyped behaviors cause significant impairment in functioning, an evaluation for stereotypic movement disorder is warranted.  There are no specific tests for diagnosing this disorder, although some tests may be ordered to rule out other conditions.

# Differential Diagnosis
Stereotypic movement disorder should be differentiated from:
- Tic disorders (Tourette's)
- Autism spectrum disorder
- Obsessive-compulsive and related disorders
- Trichotillomania
- Normal development
- Other neurological and medical conditions
Stereotypic movement disorder is often misdiagnosed as tics or Tourette's. Unlike the tics of Tourette's, which tend to onset around age six or seven, repetitive movements typically start before age 2, are more bilateral than tics, consist of intense patterns of movement for longer runs than tics.  Tics are less likely to be stimulated by excitement.   Children with stereotypic movement disorder do not always reported being bothered by the movements as a child with tics might.

# Epidemiology and Demographics

## Prevalence
The prevalence of stereotypic movement disorder is 10,000-15,000 per 100,000 (10-15%) among individuals with intellectual disability living in residential facilities of the overall population.  Stereotypic movement disorder most often affects children with mental retardation and developmental disorders.

## Gender
Stereotypic movement disorder is more common in boys.

## Age
Stereotypic movement disorder is a disorder of childhood, and can occur at any age.

# Risk Factors
- Cornelia de Lange syndrome
- Environmental stress
- Fear
- Lesch-Nyhan syndrome
- Lower cognitive functioning
- Moderate-to-severe/profound intellectual disability
- Painful medical condition
- Dental problems
- Gastroesophageal reflux
- Middle ear infection
- Rett syndrome
- Social isolation

# Natural History, Complications and Prognosis

## Natural History
Childhood habits can appear in various forms, and many people engage in some habits during their lifetime.  Habits can range from relatively benign behaviors (e.g.; nail biting) to noticeable or self-injurious behaviors, such as teeth grinding (bruxism).  Many habits of childhood are a benign, normal part of development, do not rise to the diagnostic level of a disorder, and typically remit without treatment.

## Prognosis
Prognosis depends on the severity of the disorder.  Recognizing symptoms early can help reduce the risk of self-injury, which can be lessened with medications.  Stereotypic movement disorder due to head trauma may be permanent.  If anxiety or affective disorders are present, the behaviors may persist.

# Diagnostic Criteria

## DSM-V Diagnostic Criteria for Stereotypic Movement Disorder

# History and Symptoms
The repetitive movements that are common with this disorder include:
- Thumb sucking
- Nail biting
- Nose-picking
- Breath holding
- Bruxism
- Head banging
- Rocking/rhythmic movements
- Self-biting, self-hitting
- Picking at the skin
- Hand shaking
- Hand waving
- Mouthing of objects