Commonest cause of head banging in children are

Ans. b (Mental retardation). (Ref. Nelson, 18th/116)HABIT DISORDERS##Head bangingNail biting# Body rocking# Hair pulling (trichotillomania)# Tnumb sucking# Teeth grinding (bruxism)#Hitting/biting own body# Body manipulations# Repetitive vocalizations#Aerophagia (air swallowing)# Tics Certain habit disorders are more common in children with developmental delays, particularly those with pervasive devel- opmental disorders. Self-injurious habits, such as self-biting or head banging, can occur in up to 25% of normally developing toddlers, but are almost invariably associated with developmental delays in children older than 5 yr.NOTE: Pediatric autoimmune neuropsychiatric disorder associated with streptococcal infection (PANDAS) is a condition in which antibodies to group A streptococcus cross react with basal ganglia tissue.