Neurological And Neuromuscular Disorders

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Molecular diagnosis is creating an upheaval in the classification systems of genetic neurological diseases. The spinocerebellar ataxias are now classified by at least seven subtypes depending on the molecular etiology. The nomenclature flip-flops back and forth between the hereditary motor sensory neuropathies (HMSN) and the subtypes of Charcot-Marie-Tooth (CMT) as molecular diagnosis refines the phenotypes. Many of the forms of muscular dystrophy can now be distinguished by molecular testing. This flurry of molecular advances is not only recasting the stage of how we think about neurological disorders; but molecular genetic blood tests may also save a person from invasive procedures such as muscle or nerve biopsies. The family-medical history is often the first step in decision-making for a diagnostic evaluation. Coupled with the findings from the patient's neurological exam, the medical-family history guides the clinician in choosing from the myriad of diagnostic tools available for neurological diagnosis. For references surveying the ever-changing field of neurogenetics see Emery (1998), Baraitser (1997), and the London Dysmorphology Database (refer to Appendix A.5: The Genetics Library).

Many hereditary neurological disorders are clinically complex because the nervous system is intimately intertwined with other organ systems. Table 4.14 outlines a broad approach to taking a medical-family history for a neurological condition. This section is followed by more specific guidelines for directed medical-family histories for seizures (Table 4.15), dementia (Table 4.17), and mental illness (Table 4.18). Several hereditary conditions with neurological impairment also include hearing loss (see Section 4.3) and/or visual impairment (see Section 4.4). Cardiomyopathies are common in the muscular dystrophies (see Section 4.11). Inherited metabolic disorders are a frequent inherited cause of progressive neurological conditions, particularly in children. Table 4.11 reviews some of the medical-family history indicators of an inborn error of metabolism.

TABLE 4.14 Medical-Family History Questions for Neurological Disorders*'

• Describe the problems. Are they with strength? With sensation? With weakness? With coordination? With intellect?

• What studies have been done (e.g., nerve biopsy, muscle biopsy, nerve conduction studies, spinal taps; imaging of the brain and/or spinal cord by MRI, PET, or CT scans; metabolic testing such as organic and/or amino acids, molecular testing)?

• What parts of the body are affected? For example, are there problems with weakness in the following:

Hands: Does the person drop things, or have trouble holding a pen/pencil? Feet: Does the person trip frequently, or have trouble lifting his or her feet such that they make a "slapping sound" when walking? Are the feet unusually shaped? For example, does anyone have very high arches, claw or hammer toes? (common in CMT/HMSN) Face: Are there problems with smiling, whistling, using a straw? (common in FSHMD and MMD)

Arms: Does the person have trouble lifting things?

Does the person have problems combing his/her hair? Legs: Do you notice anything unusual about the shape of the legs? (For example, unusually large calves are seen in Duchenne-Becker muscular dystrophy; thin calves are seen in the hereditary neuropathies)

• At what age did these problems begin?

• At what age did the individual begin walking? (normal is between 10 and 15 months)

• Was the individual ever able to run?

• Did (does) he or she participate in sports? Explain

• Are the problems getting worse over time or are they stable? If worse, over what period of time? (e.g., 5 years ago, past 5 months)

• Is this person able to walk on his or her own or does he or she require assistance (e.g., cane, wheelchair)?

• Is there anything unusual about the way this person looks compared to other family members? If yes, explain

• Are there other neurological disorders in this individual or in other family members, such as:

Seizures? (see Section 4.8)

Dysarthria (slurred speech)? (common in many of these disorders but particularly the hereditary ataxias) Mental retardation or learning disabilties? (see Section 4.5) Problems with thinking or judgment? (note age at onset) Problems with memory? (note age at onset) Uncontrolled movements? (common in Huntington disease) Gait disturbances? Spastic movements? Stiff movements?

Depression or mental illness? (see Section 4.10)

• Does this person or do other family members have a problem with alcohol abuse or chemical dependency?

• Does this person, or other family members, have other diseases or medical conditions?

Focus on:

Hearing loss? Note age at onset (common in NF2, several of the cerebellar ataxias, mitochondrial myopathies, associated with some forms of HMSN/CMT) (see Section 4.3)

Visual impairment? Note age at onset (Visual disturbances are frequently associated with neurological disorders, particularly retinopathies with or without mental retardation. Early onset cataracts are common in MMD) (see Section 4.4)

(continued)

TABLE 4.14 (continued)

Skeletal anomalies, including problems with posture? Short stature (see Section 4.14)

Heart disease? (particularly myopathies and cardiac conduction defects) (see Section 4.11)

Diabetes? (see Section 4.15) Thyroid disease?

Any unusual birthmarks or pigmentary changes? (common in tuberous sclerosis, NF, cerebrotendinous xanthomatosis, and some of the rarer cerebellar ataxias) Infertility? (Can be seen in men with late-onset adrenoleukodystrophy, spinobulbar muscular atrophy, and myotonic muscular dystrophy) Cancer? (An occult carcinoma may cause symptoms of an acquired ataxia)

• What is the family's ethnic background/country of origin? (For some neurological conditions there is a founder effect such that certain gene alterations are easier to identify in certain groups, or the disorder may occur more frequently in individuals of certain ancestries)

• Are the parents of the individual related as cousins or more closely related?

"Abbreviations: CMT = Charcot-Marie-Tooth disease; FSHMD = fascioscapulohumeral muscular dystrophy; HMSN = hereditary motor-sensory neuropathies; MMD = myotonic muscular dystrophy; NF = neurofi-bromatosis.

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