Selective mutism is thought to be closely related to social anxiety, as research indicates that the large majority of children with selective mutism also meet criteria for social phobia. Selective mutism is much more than normal shyness and does not reflect attention-seeking or defiant behavior. Children can appear completely unable to speak and may freeze up in some settings, as though they are afraid of others hearing their voice. Children with selective mutism often report that they want to speak but are afraid to do so.
Interference in functioning due to selective mutism can vary based on the extent to which the child fails to speak. In severe cases, selective mutism can greatly hinder a child’s social and academic functioning, as verbal communication plays a key role in these areas of development. Selective mutism typically lasts several months, but may persist for several years if left untreated. There is some evidence that symptoms remit more quickly for children who establish speech in previously mute settings at earlier ages. Reports of older children and adolescents with selective mutism are scarce, but experts in the field have noted that based on their clinical experience, individuals who enter treatment later can nonetheless make treatment gains and overcome selective mutism so that it does not continue into adulthood. In addition to comorbid anxiety disorders, particularly social phobia, it is common for children with selective mutism to have speech and language difficulties. Some children have other comorbid conditions, such as depression, panic disorder, dissociative disorders, and obsessive-compulsive disorder.
Selective mutism is now understood to be an anxiety disorder related to inhibited temperament. There is some evidence that there is a genetic contribution to the disorder, as children with selective mutism are more likely to have family members who experienced social phobia and avoidant personality disorder and parents with a history of selective mutism. On a neurobiological level, behaviorally inhibited children may have a decreased threshold of excitability in the amygdala, which is an area of the brain that receives and processes signals of potential threat and sets off a series of reactions that help individuals protect themselves. In anxious individuals, the amygdala seems to overreact and set off these responses when no danger is present. Among children with selective mutism, anxiety responses are triggered by social interactions and settings in which speaking is expected, and these children experience feelings that occur when an actual threat or danger is present. Other factors may contribute to anxiety about speaking and the development of selective mutism, including expressive language disorders and a bilingual family environment. Research does not support the claim that a history of abuse and trauma causes selective mutism. However, a stressful environment may be a risk factor in the development and maintenance of selective mutism, as it may exacerbate the child’s preexisting anxiety.