Rational diagnostic evaluation of the child with mental deficiency.

Evaluation of a mentally deficient child should be individualized, using findings from an appropriate history and physical examination. Depending on these findings the patient may be assigned to one of four subcategories, as determined by clinical indications and the patient's age at onset of the problem. These categories are (1) prenatal problem of morphogenesis, (2) perinatal insult to brain, (3) postnatal onset of brain dysfunction, and (4) undecided age at onset. This subcategorization has revelance to the type of diagnostic studies that may be indicated. Using this approach, a retrospective study of the diagnostic evaluation of 98 mentally deficient children was performed. Ninety percent of these children were considered to have had "nonrational" laboratory tests, and of these, none contributed to elucidation of the basic diagnosis. The only tests that were valuable had been indicated by a specific historical or physical finding in addition to mental deficiency.