Childhood Habit Behaviors and Stereotypic Movement Disorder 

Childhood habits appear in many different forms. Many people engage in some degree of habitlike behavior in their lifetime. For example, habits can range from seemingly benign behaviors, such as nail biting or foot tapping, to more noticeable physically damaging behaviors, such as teeth grinding (bruxism) and hair pulling. Habit disorders, now subsumed under the diagnostic term stereotypic movement disorder, consist of repetitive, seemingly driven, and nonfunctional motor behaviors that interfere with normal activities or that result in bodily injury. Fortunately, many childhood habits are benign, they are considered a normal part of development, they do not meet the criteria for a disorder, and they typically remit untreated.

The Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV), formerly used the term stereotypy/habit disorder and now uses the term stereotypic movement disorder to designate repetitive habit behaviors that cause impairment to the child.^[1]

This review focuses on a number of common childhood behaviors, including thumb sucking, nail biting, nose picking, breath holding, bruxism, head banging, and rocking and/or rhythmic movements. In mild forms, some of these behaviors do not interfere with normal daily activities and, therefore, do not constitute psychiatric disorders. However, mild forms of these behaviors can progress to cause functional impairment or physical and/or psychological sequelae or stigmatization. When functional impairment is substantial, the diagnosis of stereotypic movement disorder should be considered.

The differential diagnosis of stereotypic movement disorder requires the clinician to rule out a number of other psychiatric conditions in which repetitive behaviors are core features. Examples include obsessive-compulsive disorder, trichotillomania, vocal and motor tics, and Tourette disorder. When these disorders best account for symptoms, stereotypic movement disorder is not diagnosed.

Some childhood habits remain unnoticed and can persist untreated, even when they interfere with the child's optimal functioning. Childhood habits can result in negative social interactions and avoidance by peers and family members. Some repetitive behaviors can cause damage. For example, teeth grinding (bruxism) can result in tooth damage. Occasional hair pulling can result in hair loss or evolve into the more severe disorder, trichotillomania. However, for most children who are otherwise developing normally, few habits result in permanent physical damage to the child. In some cases, treating a childhood habit before clearcut dysfunction arises may prevent serious psychopathology and social dysfunction. Much of what is known about childhood habits derives from the literature about common habit behaviors in adults.

The pathophysiology of specific habits varies greatly with respect to the topography and frequency of the particular habit behavior.

• Thumb sucking: Thumb sucking is an oral habit that involves mouthing of the thumb. Other fingers or the hand may also be involved.
• Nail biting: Nail biting consists of biting on or chewing the nails of the hand.
• Nose picking: Nose picking is the insertion of a finger into a nostril and may involve the removal of nasal discharge (ie, snot, "boogers"). Older children and adults are most likely to pick their nose in private, whereas young children may commonly do this in public view.
• Bruxism: Bruxism is the forcible gnashing, grinding, clicking, or clenching of teeth. Nocturnal bruxism occurs during sleep, and the child is usually unaware of the problem. Episodes are typically brief, lasting 8-9 seconds, with audible grinding noises. Diurnal (daytime) bruxism is primarily associated with clenching of the teeth and generally does not produce audible noises. Diurnal bruxism is related to other oral habits, such as nail biting or lip chewing.
• Breath-holding spells: A breath-holding spell is a paroxysmal event in which a child stops breathing at end-expiration after crying, typically because of pain or anger. The crying may be brief or prolonged. Breath-holding spells are classified as simple, cyanotic, or pallid. A simple breath-holding spell results when the child becomes apneic (cyanotic or pale) but then takes a deep breath. Spells with loss of consciousness and muscle tone are classified by the child's color during the event. Cyanotic spells typically have an emotional precipitant (eg, anger, frustration), and with breath holding, the child progresses from cyanotic to apneic. The child may then become limp and lose consciousness.
• The spell typically lasts less than 1 minute. If a seizure occurs, the results from an electroencephalograph (EEG) obtained during rest or sleep are normal. Pallid spells are generally observed in response to pain, and the child quickly becomes apneic and pale. An enhanced vagal response has been postulated to be a precursor to bradycardia or asystole. Seizures rarely result.
• Head banging: Head banging is the rhythmic hitting of the head (usually the frontal or parietal region) against a solid surface. In children who are developmentally normal, it usually lasts less than 15 minutes but can last hours. A high frequency of up to 60-80 hits per minute is common. It can be associated with temper tantrums, tension, or stress. Head banging can also develop as a sleep ritual if the head banging occurs as the child falls asleep.
• Body rocking or rhythmic movements: Body rocking usually involves a forward and backward rhythmic swaying of the trunk at the hips, generally from a sitting or quadruped position. The intensity may be gentle, or it may be forceful enough to move the child's crib or bed. This behavior typically occurs when children are alone in their cribs or beds. Most episodes last less than 15 minutes but may persist up to 30 minutes. Rhythmic or stereotypic behaviors include repetitive nonfunctional motor movements, such as hand flapping or shaking, self-biting, or hitting one's own body.

Frequency

United States

Accurate prevalence rates of childhood habits are extremely difficult to estimate because of the various classes of habits and the differing topographies of a child's presenting habit. The prevalence rates of habit disorders are at best unclear, and some remain unknown among children. Future studies will hopefully reveal a more accurate picture of the number of children with the various childhood habit disorders. Estimates from the literature for various types of common habit disorders appear below.

• Thumb sucking: This is common in infancy and in as many as 25-50% of 2-year-old children. However, it is observed in only 15-20% of 5- to 6-year-old children.
• Nail biting: This is mainly observed from preschool age to adolescence; the prevalence is as high as 45%-60%.
• Nose picking: Few studies have been performed. However, in 1 survey, as many as 91% of adults reported nose picking.
• Breath-holding spells: These are common in up to 4-5% of children younger than 8 years.
• Bruxism: This is observed in 5-30% of children.
• Head banging: This can occur in 3-19% of developmentally normal children younger than 3 years. It is more frequently observed in children with autism or developmental delay and in those living in institutional environments.
• Body rocking and rhythmic movements: These occur in most infants aged 6-12 months. The behavior is most often observed in children with developmental disabilities or sensory impairments; however, it persists beyond age 2 years in 3% of children with normal development.

The age of onset and resolution of habit behaviors may be delayed in children with developmental disabilities.

Stereotypies are observed in 40-60% of individuals who are institutionalized and have profound mental retardation, 8-10% of individuals who live in the community and have moderate mental retardation, and up to 20% of individuals who live in the community and have mental retardation and autism. Self-injury is less common; it is observed in 10-20% of individuals who are institutionalized and have mental retardation, 1-3% of individuals who live in the community and have moderate mental retardation, and up to 5% of individuals who live in the community and have mental retardation and autism.

Mortality/Morbidity

Because childhood habits take various forms, a wide range of mortality and morbidity profiles exist. Mortality is extremely rare.

• All habits have the potential to produce social stigmatization and distress depending on the environmental context in which they occur.
• Although the range of physical sequelae varies greatly, serious medical complications are rare.
• Some habit disorders may not directly cause the child observable physical damage. Instead, they may result in impairment in social functioning. Stigmatization resulting from the habit can cause the child considerable distress, humiliation, social rejection, academic problems, feelings of shame and guilt, discomfort in social activities, and depression or anxiety.

Sex

Just as the overall prevalence rates of childhood habits are unknown, data on sex-based differences in prevalence are limited at best. In cases of self-injurious behavior, head banging is believed to occur 3 times more frequently in male individuals than in female individuals. Self-biting may be more prevalent in female individuals than in male individuals.

• Thumb sucking: This is suspected to occur slightly more often in girls than in boys.
• Nail biting: This tends to be more common in females than in males.
• Nose picking: Sex-based differences in nose picking are unknown.
• Bruxism: When the types of bruxism are separated into clenching and grinding, more females than males grind their teeth, but the number of males and females who engage in teeth clenching are equal. In addition, resulting dysfunction of the temporomandibular joint (TMJ) may be more common among female adolescents than male adolescents.
• Breath-holding spells: The occurrence among boys and girls is equal.
• Head banging: This occurs 3 times more often in boys than in girls.
• Rocking and rhythmic movements: Sex-based differences in rocking and rhythmic movements are unknown.

Age

The age at which specific habits originate, peak, and remit is related to the individual habit behavior.

• Thumb sucking: This is observed in utero as early as 29 weeks' gestation. It is common in infancy and is observed in as many as 25-50% of children aged 2 years. Rates of thumb sucking declines with increasing age; most children spontaneously stop at about 4 years of age. It is observed in only 15-20% of children aged 5-6 years.
• Nail biting: Onset in children younger than 4 years is rare. Rates as high as 45-60% are observed in preschool age to adolescence.
• Nose picking: This is common in adults and children.
• Bruxism: Bruxism is observed in 5-20% of children. The frequency increases during childhood, peaking at 7-10 years of age and decreasing after that. It is common in children and adults.
• Breath-holding spells: These are reported to occur in 4-5% of the pediatric population, with a peak in frequency at 2-3 years. Breath-holding spells may begin as early as infancy. Approximately 80-90% of preschoolers with breath-holding spells stop by age 6 years.
• Head banging: This can occur in 3-19% of developmentally normal children younger than 3 years. It peaks at the ages of 18 months to 2 years, and rates rapidly decline after that. Head banging continues in 1-3% of children older than 3 years. The behavior can recur at 5-6 years of age. Head banging is more frequently observed in children with autism or developmental delay or in those living in an institutional environment.
• Body rocking and rhythmic movements: These occur in most infants aged 6-12 months. The prevalence peaks in children aged 6-18 months and rapidly declines after that. The behavior persists beyond age 2 years in 3% of children with normal development. Body rocking and rhythmic movements are most often observed in children with developmental disabilities or sensory impairments and may be associated with a lack of environmental stimulation.