Differential Diagnosis of ADHD in School-Age Children

Adelaide S. Robb, MD


September 26, 2006

In This Article

Primary Inattentive Subtype

The child with primary inattentive subtype of ADHD tends to present with problems later, sometime between the third and sixth grade. Symptoms of primary inattention include difficulty sustaining attention, making careless mistakes, easy distractibility, forgetfulness, not listening when spoken to, losing things, avoiding tasks, not finishing tasks, and poor organization.[3] These symptoms usually lead to a decline in academic performance during third grade or later, when academic work requires the synthesis of materials and organizational skills needed for long-term projects and papers. The differential includes both psychiatric and nonpsychiatric disorders.

Possible psychiatric conditions include language and learning disabilities, anxiety disorders, affective disorders, adjustment disorders, and psychotic disorders. Medical maladies include epilepsy, neurologic disorders such as neurofibromatosis, thyroid dysfunction, sleep disorders, toxic insults to the central nervous system (CNS), medication adverse effects, and infectious diseases.[4,5]

Children with subtle receptive language processing disorders may look inattentive because they cannot understand the classroom instructions. Children with learning disabilities may also start to struggle after third grade because the more complex learning tasks present greater challenges.

Several anxiety disorders, including GAD, separation anxiety disorder, PTSD, panic disorder, social phobia, and OCD, may all be characterized by poor classroom performance and difficulty paying attention; some children may even demonstrate mild psychomotor agitation. Inquiring whether the child worries about anything usually elicits a long list of worries and preoccupations that easily differentiates the anxious child from the ADHD child.

Depression, with its accompanying psychomotor retardation, lack of energy, and poor attention and concentration, imitates inattentive ADHD. However, the depressed child is sad and tearful, and experiences changes in appetite, sleep, and energy in addition to the cognitive difficulties. Adjustment disorders that include depressed or anxious mood may also resemble inattentive ADHD; this child will have experienced a recent stressor in his or her life and a marked and rapid change in academic functioning.

Occasionally, children who present for an evaluation for inattentive ADHD have psychotic disorders including schizophrenia. A careful interview will reveal that the child has odd behaviors and beliefs, delusions, or hallucinations, and seems internally preoccupied.

Medical disorders that mimic inattentive ADHD symptoms must be fully evaluated with laboratory testing, physical examination, and physiologic monitoring. Absence and simple partial epilepsy can present with staring spells or missing parts of the school day as a result of the seizures. An electroencephalogram should be performed to rule out epilepsy as a cause of these inattention and staring spells.

Children with sleep disorders that interrupt REM and non-REM sleep, including sleep apnea, restless legs syndrome, and other sleep disorders, may present with inattention and poor school performance. In addition, some middle school children suffer a chronic lack of sleep and will be inattentive and "spacy" because of sleep deprivation. A sleep history and a sleep study can rule out sleep disorders as a cause of inattention and school difficulties. Some children with obstructive sleep apnea may show improvements in ADHD symptoms after a tonsillectomy and adenoidectomy.[6]

Children with neurofibromatosis may begin to have difficulties in elementary school with problems beginning when the lesions appear in the brain. A physical examination would reveal café au lait spots and cutaneous neurofibromas. Genetic testing for the disorder is confirmatory.

Certain heavy metal toxicities, especially lead poisoning, may lead to problems with attention and concentration and can be evaluated with a lead screen. Treatments for childhood cancers, including central nervous system irradiation and intrathecal chemotherapy, may lead to neurocognitive side effects that imitate the symptoms of ADHD but were not present before age 7. These behaviors are the result of a CNS insult rather than a primary psychiatric illness. Certain medications, including antihistamines, benzodiazepines, selective serotonin reuptake inhibitors, and antiepileptic drugs, may cause inattention and hyperactivity.

Children with vertically transmitted HIV infection may have difficulties with attention and school performance because of the infection or an associated subcortical dementia. Children with undiagnosed Lyme disease also can present with attention and concentration difficulties. Those children who are at risk for HIV or Lyme disease and who present during middle school with new-onset ADHD should be screened for those infections.


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