'Specific developmental disorders of scholastic skills' (ICD-10) or 'Learning disorders' (DSM-IV) include disorders characterized by one or more significant impairments in acquisition of reading, spelling, or arithmetical skills. ICD-10 suggests that the category 'Mixed disorder of scholastic skills' (F81.3) be used as an ill-defined, but necessary, category in which arithmetical and reading or spelling skills are significantly impaired, although not because of general mental retardation or inadequate schooling.
The disorders classified in the category 'Specific developmental disorders of scholastic skills' ( SDDSS) resemble specific disorders of speech and language. As in these latter disorders, normal patterns of skill acquisition are disturbed and detectable at an age when these functions are required. The disorders are not due to a lack of opportunity to learn or a consequence of brain trauma or disease, but represent a specific type of dysfunction in cognitive processing. The dysfunction affects specific skills, which can be distinguished from the cognitive functions that are usually in the normal range. As in other specific developmental disorders, the condition is more common in boys than in girls.
ICD-10 notes five difficulties regarding diagnosis and differential diagnosis:
1. differentiation of the disorder from normal variations in scholastic achievement (this problem applies to all specific developmental disorders and was discussed in relation to specific developmental disorders of speech and language);
2. consideration of the normal developmental course;
3. interference with learning and teaching;
4. underlying abnormalities in cognitive processing;
5. uncertainties over the best way of subdifferentiating SDDSS.
Based on these considerations, the following diagnostic guidelines for all SDDSS have been suggested (ICD-10):
• Clinically significant degree of impairment: this is judged on the basis of severity (e.g. occurrence in less than 3 per cent of schoolchildren), developmental precursors (e.g. speech or language disorder in preschool years), and associated problems (e.g. inattention).
• Specific impairment not explained solely by mental retardation or by lesser impairments in general intelligence: for this requirement to be met, individually administered and standardized IQ scholastic achievement tests are obligatory to demonstrate that the child's level of achievement is substantially below the expected level compared to a child of the same mental age.
• Developmental nature of the impairment: this must be demonstrated by the presence of the disorder during the early years of schooling and by exclusion of impairment acquired later. The child's history of school progress is decisive in this respect.
• Absence of external factors that could explain the impairment: SDDSS are thought to be mainly based on factors intrinsic to the child's development, and not due to inadequate schooling or any other environmental factors such as absence from school or educational discontinuities. However, such conditions may occur, making the diagnostic process difficult.
• Exclusion of visual and hearing impairments: by definition, SDDSS do not occur as a result of impairment of sensory function, such as visual or hearing impairment.
The main differential diagnostic task is distinguishing SDDSS from neurological disorders or impairments that may also be responsible for the impairment of scholastic skills (e.g. alexia, aphasia, agraphia, apraxia). In cases of normal child development prior to the manifestation of a defined neurological disorder, differential diagnosis is not difficult. However, if minor neurological signs (soft signs) were diagnosed previously, independent of any defined disorder, and the findings persist, it may be difficult to distinguish recent symptoms from previous ones. In such cases, associated disorders or symptoms should be classified separately in the appropriate neurological section of the classification systems.
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