Matthew D. Jacofsky, Psy.D., Melanie T. Santos, Psy.D., Sony Khemlani-Patel, Ph.D. & Fugen Neziroglu, Ph.D. of the Bio Behavioral Institute, edited by C.E. Zupanick, Psy.D. and Mark Dombeck, Ph.D.
Selective Mutism occurs when a child or adult persistently refuses to speak in specific situations where speaking is expected. For instance, a child might speak at home with family members, but will not speak at all to teachers or peers at school. The diagnosis is more commonly applied to children. According to DSM-5 criteria (APA, 2013), the symptoms must last at least one month. It must be clear that the child's refusal to speak is not the direct consequence of some other disorder.
Selective Mutism is a relatively rare disorder occurring in less than 1% of the population (APA, 2013). These prevalence data may not be entirely accurate because many people are unfamiliar with the problem. As a result, some children with Selective Mutism may go undiagnosed and untreated. This disorder has been well documented with cases dating back to the 19th century. However, despite its long history, the disorder is not well understood. Debate continues regarding its causes and proper classification.
Children with Selective Mutism frequently demonstrate shyness, anxiety, and fears of embarrassment and negative evaluation. Children may isolate themselves socially, withdraw from peer interactions, or cling to parents and other "safe" figures. In addition, they may demonstrate frequent temper tantrums and other negative or compulsive and controlling behaviors. Some children will engage in oppositional behaviors, especially within the home. Children with Selective Mutism may substitute gestures and other non-verbal forms of communication for spoken language. Many of these symptoms overlap with Social Anxiety Disorder. However, Social Anxiety Disorder requires that the symptoms must occur in the context of peer interactions, and the symptoms must have endured for 6 months or longer. A person may receive both diagnoses.
The course of Selective Mutism is variable across individuals. Some children will remain selectively mute over several years. Other children will start talking after a few months.