There are three types of attention deficit hyperactivity disorder -- ADHD -- affecting both children and adults. People affected with ADHD are either predominantly hyperactive-impulsive, predominantly inattentive or have a combined form of the disorder, exhibiting symptoms of both of the hyperactive-impulsive and the inattentive type. According to the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders -- DSM, in order to diagnose ADHD, symptoms must have been present before the person was age 12. However, ADHD is often diagnosed in adolescents or adults years later.
Hyperactive children and adults may express hyperactivity differently. Hyperactive children may run around in circles until they drop from dizziness. Adolescents and adults are more restrained and their hyperactivity may be expressed by jiggling their legs or pacing. Impulsivity also may be expressed differently. Both children and adults with ADHD may have trouble waiting in line. The child may try to cut ahead while the adult is more likely to fidget or mutter in place. Both children and adults with ADHD may blurt out thoughts when inappropriate.
Individuals with the inattentive form of ADHD may seem to have their "head in the clouds." Often they're late meeting others because they were distracted by something interesting and forgot all about the prearranged meeting. They frequently lose items because they set them down and immediately forget where. They fail to finish projects because a new project seems far more interesting. When intrigued by a project, people with inattentive ADHD may concentrate actively and for long periods. They may lose track of time and fail to pick up a child at school or complete a less interesting homework assignment. This is called "hyperfocusing."
Listening is hard for people with this form of ADHD, because they're attending to their own constantly shifting thoughts rather than what's said by a teacher or the boss. They may pretend they heard and understood, but are "found out" when questioned.
Inattentive children may have difficulty or delays with reading and math. They may be very bright but cannot sustain sufficient attention to master these skills. This can have repercussions into adulthood; for example, the child may believe he is "stupid," affecting life choices.
Disorganization is a problem for many people with ADHD and may be reflected in clutter and disarray. Often this disorganization is another factor in the loss of personal items. Children and adults with the inattentive form of ADHD may fail to perceive the presence of clutter because of their own distractibility and inattentiveness.
Just like it sounds, children and adults with the combined form of ADHD have characteristics of both the hyperactive-impulsive type and the inattentive type of ADHD. They may be hyperactive and distractible or impulsive and disorganized. According to the DSM, most children and adolescents with ADHD have the combined type, but it is unknown if this is true in adults with ADHD.