Selective mutism is a type of anxiety disorder whose main distinguishing characteristic is the persistent failure to speak in specific social situations (e.g., at school or with playmates) where speaking is expected, despite speaking in other situations.
Selective mutism interferes with educational or occupational achievement or with social communication, and in order for it to be diagnosed, it must last for at least 1 month and is not limited to the first month of school (during which many children may be shy and reluctant to speak).
Selective mutism should not be diagnosed if the individual’s failure to speak is due solely to a lack of knowledge of, or comfort with, the spoken language required in the social situation. It is also not diagnosed if the disturbance is accounted for by embarrassment related to having a communication disorder (e.g., stuttering) or if it occurs exclusively during a pervasive developmental disorder, schizophrenia, or other psychotic disorder. Instead of communicating by standard verbalization, children with this disorder may communicate by gestures, monosyllabic, short, or monotone utterances, or in an altered voice.
Associated features of selective mutism may include excessive shyness, fear of social embarrassment, social isolation and withdrawal, clinging, compulsive traits, negativism, temper tantrums, or controlling or oppositional behavior, particularly at home. There may be severe impairment in social and school functioning. Teasing or scapegoating by peers is common. Although children with this disorder generally have normal language skills, there may occasionally be an associated communication disorder (e.g., phonological disorder, expressive language disorder, or mixed receptive-expressive language disorder) or a general medical condition that causes abnormalities of articulation.
Immigrant children who are unfamiliar with or uncomfortable in the official language of their new host country may refuse to speak to strangers in their new environment (which is not considered selective mutism).
Selective mutism seems to be rare, being found in fewer than 0.05 percent of children seen in general school settings. Selective mutism is slightly more common in females than in males.
Criteria summarized from: Diagnostic and statistical manual of mental disorders, fifth edition. Washington, DC: American Psychiatric Association.