Autism (autism spectrum disorders) is a complex, strongly genetically influenced, behaviorally defined disorder of the immature brain associated with very uneven intellectual abilities. Among its most salient and potentially treatable neurologic features that this article focuses on are epilepsy, disorganized sleep patterns, and sensory and motor deficits. Its many causes and wide range of severity means that there is no symptom, no pathology, imaging, electroencephalography, or other biologic feature, and no biologic treatment that is universal or diagnostic of this developmental syndrome.
Diagnostic issues
Autism, used here as short for autism spectrum disorders (ASDs), is not a disease as it does not have a unique biologic cause. It is a behaviorally defined syndrome of early life, with varied symptoms reflecting many biologic and environmental influences that are unique to each individual’s brain and that shape its unique developmental trajectory. The goal of neurologic, genetic, electrophysiologic, imaging, and other biologic tests performed on some of the children is not to diagnose autism but to attempt to define some of its many potential etiologies and understand their pathogenic effects on the brain.
Currently, the defining deficits of ASDs involve social skills, communicative language and imagination, and narrowness of focus resulting in rigidity, preoccupations, and repetitive movements (motor stereotypies) and speech. People with autism have many other symptoms besides these core characteristics, in particular uneven intellectual abilities, depending on the extent and distribution of their affected brain circuitry.
The diagnosis of autism and its subtypes is dimensional, not dichotomous (yes/no). It is based on the severity of affected individuals’ symptoms, for example number of aberrant behaviors endorsed on a standardized checklist or clinical evaluation. Diagnostic cutoffs were arrived at by multidisciplinary field trials. As in obesity, diabetes, and many other multifactorial conditions, there is quasiunanimous diagnostic agreement about persons at the center of the bell-shaped severity distribution. However, this is not the case for those in its 2 tails, where diagnostic margins are inherently fuzzy. At the lower end, where underlying brain dysfunction and intellectual impairment are severe, there is so much overlap between the autistic and intellectual deficits that deciding whether or not autism applies as the main diagnosis is contentious. At the upper end, especially when the autism is mild and intelligence is average or greater than average, there may be so much overlap with normalcy that the diagnosis of autism is often equivocal and, in some cases, a matter of expediency. Despite their inherent lack of rigorous yes/no diagnostic criteria, well-defined and agreed upon dimensional criteria have improved the diagnostic consistency of both medical and behavioral disorders. It is essential to keep in mind that autism is behaviorally defined and has no unique biologic cause. Consequently no single sign, symptom, clinical feature, and no specific cause (biologic or environmental etiology), gene, or neuropathology invalidates its diagnosis.
In the October 2008 issue of the Pediatric Clinics concerned with developmental disabilities, members of our group discussed the differential diagnosis of autism. In this contribution, we focus on clinical evidence regarding its main neurobiological basis, anatomy and imaging, epilepsy, disturbed sleep patterns, and sensorimotor symptoms.
The brain in autism
In most cases, the cause of the ASD remains unidentified and can not be found within the anatomic, radiographic, electroencephalographic (EEG), biogenetic, or pathologic evidence that neurologists routinely depend on for clinical diagnosis. Newer research evidence points to the need for more data at the brain network, cellular, and biochemical levels if the common pathophysiology that links the multiple genetic and nongenetic disorders that underlie the ASDs is going to be understood ( Table 1 ).
