Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (76 page)

Thrombophlebitis of Cavernous Sinus

Spinal Cord Infarction

CNS Vasculitis

Paraneoplastic Syndromes Affecting the CNS

Myasthenia Gravis

Lambert-Eaton Myasthenic Syndrome

Infections of the Central Nervous System

Central Nervous System Abscesses

Encephalitis

Meningitis

In the 10th edition, this Chapter has been updated to present the laboratory workup of neurologic diseases by primary presenting symptomatology and expanded to provide a thorough differential diagnosis. Please remember that many disorders overlap in their presenting signs, and these will be cross-referenced when possible. Evaluation of the nervous system requires a multidisciplinary approach to the patient and, where appropriate, pertinent clinical findings, radiologic procedures, and laboratory tests have been included to aid in the diagnosis. Please see the e-book version for the figures referenced in this Chapter.

DISORDERS OF COGNITION AND DEMENTIA

INTELLECTUAL DISABILITY

   Definition

Intellectual disability (ID) is defined by the DSM-IV
¹
as significant subaverage intellectual function, significant limitations in adaptive functioning, and onset before 18 years. It is an unchanging encephalopathy that may be due to a number of disorders that affect brain development and function.

   Clinical Presentation

Developmental screening with standard screening tools should be performed at every well-child visit. A comprehensive history and physical should include measurements of height, weight, and head circumference, including growth velocity, dysmorphic features, neurologic and sensory development, and a detailed observation of behavior.

   Causes

Prenatal

Genetic causes are the most common forms of ID in the prenatal group. Current testing for fetal trisomies and a number of other known genetic disorders is routinely carried out as part of the prenatal screen. Amniotic fluid or chorionic villi sampling may be used for microarray or chromosomal analyses, and maternal blood may now be tested by cell-free DNA methods. Chromosomal disorders resulting in ID include Down syndrome; trisomy 18; fragile X; autosomal recessive genes PRSS12, CRBN, CC2D1A, TUSC3, GRIK2, and SYNGAP1; autosomal dominant genes STXBP1, SYBGAP1, and SCN2A; cri-du-chat syndrome; and Klinefelter syndrome
^2–4
(See Chapter
10
Hereditary and Genetic Diseases).

Nongenetic prenatal causes include the following:

   CNS malformations

   Congenital infections (e.g., syphilis, rubella, toxoplasmosis, CMV) resulting in hydrocephalus (see eBook Figure 4-1)

   Metabolic abnormalities (e.g., DM, eclampsia, placental dysfunction)

   Environmental toxins or teratogens (alcohol, lead, mercury, hydantoin, and valproate) and radiation exposure

   Metabolic abnormalities (congenital hypothyroidism)

   Amino acid metabolism (e.g., phenylketonuria, maple syrup urine disease, homocystinuria, cystathioninuria, hyperglycemia, argininosuccinicaciduria, citrullinemia, histidinemia, hyperprolinemia, oasthouse urine disease, Hartnup disease, Joseph syndrome, familial iminoglycinuria)

   Lipid metabolism (e.g., Batten disease, Tay-Sachs disease, Niemann-Pick disease, abetalipoproteinemia, Refsum disease, metachromatic leukodystrophy) resulting in abnormal storage disorders (see eBook Figure 4-2)