Evaluation Guidelines Table156

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A wide variety of tests are now available to the neurological clinician. The work-up must be tailored to the situation and guided by a careful analysis of the neurological examination and history. The findings on the neurological examination localize the lesion to the nervous system and to the area where the attention should be focused. They also narrow the possible causes of the disorder. The list of possible causes is narrowed further by the history, which gives the clinician the temporal profile of the disease process.

Neuroimaging. Neuroimaging has become a powerful tool in confirming the localization of lesions. Magnetic resonance imaging (MRI) is the most powerful imaging tool available, but in some cases computed tomography (CT) is equally effective (e.g., in some tumors) or better (e.g., bony abnormalities, hemorrhage) in visualizing the lesion. Because it has a much higher resolution and is not subject to artifact from neighboring bony structures, MRI is the test of choice for imaging the posterior fossa. MRI is also the tool of choice for visualizing the spinal canal

TABLE 15-6 -- USEFUL STUDIES FOR THE EVALUATION OF DISORDERS OF MUSCLE STRENGTH AND REFLEXES

Neuroimaging

Electrophysiology

Fluid and Tissue Analysis

Neuropsychological Tests

UPPER MOTOR NEURON SYNDROMES

Pyramidal lesions

Cortex and subcortex

MRI or CT of brain: lesion contralateral to hemiparesis

N/A

CSF pressure

Lateralized right or left hemisphere dysfunction

Left: tests of language, praxis

Right: tests of construction, spatial orientation

Brain stem

MRI: local lesion

N/A

N/A

N/A

Spinal cord

MRI or CT myelography:

Somatosensory evoked potentials (SSEP):

CSF: protein, glucose, IgG, WBC,

N/A

extrinsic versus intrinsic lesion

delayed conduction with median or tibial nerve stimulation

RBC count

Decerebrate and

MRI or CT scan: lesion in

N/A

N/A

N/A

decorticate posturing

midbrain (decerebrate); bilateral hemisphere (decorticate)

Diffuse excitation of

N/A

EMG: continuous motor potentials

Blood and CSF: GABA, GAD

N/A

internuncial pool

autoantibodies (stiff-person syndrome)

LOWER MOTOR NEURON SYNDROMES

Progressive spinal

MRI: atrophy of spinal cord

EMG: denervation-fibrillations,

Muscle biopsy: grouped atrophy

N/A

atrophy syndrome

(late stages)

fasciculations, positive sharp waves, giant

Blood: DNA analysis

MUAPs

Radiculopathy

MRI or CT myelography: compression of nerve root by disc or bony spur

EMG: denervation potentials in muscles supplied by affected root

Blood: FBS

N/A

Plexopathy

MRI: infiltrating mass

EMG: denervation of muscles supplied by multiple roots

Blood: FBS, ESR, SR, ANA, SPEP

N/A

Peripheral

N/A

EMG/NCV: abnormal nerve conduction of

Nerve biopsy: inflammation,

N/A

neuropathy

affected nerve results in denervation of

demyelination

Mononeuropathy

muscle supplied by that nerve

Blood: ESR, ANA, SPEP, FBS

Polyneuropathy

N/A

EMG/NCV: abnormalities of all nerves; legs affected before arms

CSF: protein

Nerve biopsy: inflammation, demyelination, amyloid

Blood: ESR, ANA, SPEP, FBS, B12 , T4/TSH, anti-nerve antibodies

N/A

COMBINED UPPER AND LOWER SYNDROMES

Motor neuron disease

MRI: cervical cord-may be

EMG: denervation with giant MUAPs,

Muscle biopsy: grouped atrophy

N/A

atrophic

normal NCV

Blood: CK normal to mildly elevated

Myelopathy

MRI, CT myelography

Somatosensory evoked potentials

Visual evoked potentials (if multiple sclerosis is suspected)

CSF: protein, IgG, oligoclonal bands, inflammatory cells

Blood: VDRL, B,2, long chain fatty acids

N/A

Spinal shock

MRI, CT myelography

N/A

N/A

N/A

NEUROMUSCULAR JUNCTION SYNDROMES

Myasthenia and

Chest CT

EMG: decremental response to repetitive

Blood: acetylcholine receptor

N/A

botulism

nerve stimulation

antibodies Botulinum toxin

Eaton-Lambert

Chest x-ray, mammography,

EMG: incremental response to repetitive

Blood: striated muscle antibodies

N/A

syndrome

pelvic ultrasound

nerve stimulation

MYOPATHIC SYNDROMES

Myopathy

N/A

EMG: small-amplitude polyphasic MUAPs

Skin/muscle biopsy: inflammation, mitochondrial abnormalities, necrosis and fibrosis, histochemical analysis

Blood: CK, ESR

N/A

MRI, Magnetic resonance imaging; CT, computed tomography; EMG, electromyography; CSF, cerebrospinal fluid; WBC, white blood count; RBC, red blood count; GABA, gamma aminobutyric acid; GAD, glutamic acid decarboxylase; DNA, deoxyribonucleic acid; NCV, nerve conduction velocity; MUAP, motor unit action potential; FBS, fasting blood sugar; SR, sedimentation rate; ANA, antinuclear antibodies; SPEP, serum protein electrophoresis; eSr, erythrocyte sedimentation rate; B12 , vitamin B12 ; T4/TSH, thyroxine-thyroid-stimulating hormone; VDRL, Venereal Disease Research Laboratory; CK, creatine kinase; IgG, immunoglobulin G; N/A, not applicable.

except in circumstances (e.g., cervical spondylosis, vascular malformations) when myelography with CT may be superior for identifying the extent of the root or cord involvement. Conventional radiographs of the spinal column may be indicated when infectious, neoplastic, degenerative, or developmental disorders of bone are suspected.

Electrophysiology. Electromyography and measurement of nerve conduction velocities can be crucial in identifying, localizing, and determining the extent and severity of disorders in the lower motor neuron unit. The electromyographer still needs guidance from the history and neurological examination to tailor his evaluation to the appropriate region and choose the proper test to gain accurate and confirmatory observations most efficiently. With these tools, it is possible to differentiate an anterior horn cell disorder from a lesion of the spinal root or nerve or to differentiate disorders of the neuromuscular junction from primary muscle disease.

Fluid and Tissue Analysis. Examination of the cerebrospinal fluid (CSF) via a lumbar puncture has been one of the standbys in neurological diagnosis. Because it is virtually identical in composition to the extracellular fluid, changes in the chemical or cellular composition of CSF can reflect a variety of diseases. Analysis of the CSF is most useful in diagnosing subarachnoid hemorrhages or infections and inflammatory disorders that produce an excess of white cells or changes in immunoglobulin.

Tests for specific bacterial and fungal antigens are now available for diagnosing the more common bacterial (e.g., influenza, pneumococcal, meningococcal) or fungal (e.g., cryptococcal) meningitides. Polymerase chain reaction (PCR) tests for certain viruses are now available. It is no longer necessary to perform a brain biopsy to diagnose herpes simplex encephalitis.

Immunohistochemical techniques have made muscle biopsy even more useful in diagnosing any disorder affecting muscle including mitochondriopathies. Nerve biopsies are usually less informative and are generally useful only in patients with inflammatory disorders affecting the nerves or their blood supply, or in those with amyloidosis for detecting the deposition of amyloid.

Except as a tool for making a diagnosis of a tumor or abscess, brain biopsy is used sparingly to diagnose rare encephalitides (e.g., Creutzfeld-Jakob disease) or vasculopathies (e.g., granulomatous angiitis).

Neuropsychological Tests. If cerebral lesions are suspected, neuropsychological testing may identify evidence of a single, multifocal, or diffuse process. Special tests for aphasia, apraxia and spacial orientation identify and lateralize cortical lesions.

Other Tests. Edrophonium chloride (Tensilon), a short- acting cholinesterase inhibitor, is used in the diagnosis of myasthenia gravis (Tensilon test). As explained earlier in the discussion of fatigability, a symptomatic muscle that is most amenable to semiquantitative testing is chosen for the measurement of fatigability before and after the intravenous injection of edrophonium. This test is sometimes done in conjunction with injection of a saline placebo. However, because muscarinic as well as nicotinic receptors are stimulated by the accumulation of acetylcholine in the synaptic cleft, this test is difficult to perform in a blinded fashion because intestinal cramping and muscle fasciculations in the eyelids are generally produced by the edrophonium. The muscarinic effects may also cause a bradycardia that is sufficiently severe to induce fainting, and rarely asystole occurs in what appears to be an idiosyncratic reaction. Therefore, a small test dose of 0.2 ml is given first to assess for an idiosyncratic reaction before the remaining 0.8 ml is given. The effects are short lasting but are long enough to assess strength in the muscles chosen for testing. A positive test (i.e., a significant improvement in muscle strength), is consistent with myasthenia gravis.

A forearm ischemia test is used to diagnose disorders of energy production in muscle. This test is especially useful

TABLE 15-7 -- SELECTED ETIOLOGIES OF CONDITIONS THAT AFFECT STRENGTH AND REFLEXES

Etiological Category

Specific Etiologies

Chapter

STRUCTURAL DISORDERS

Developmental

Hydrocephalus; neural tube defects; segmentation, cleavage and midline defects, neuronal migration defects

28

Degenerative and compressive

Degeneration disc disease; cervical spondylosis; ankylosing spondylitis; fibrous dysplasia; Paget's disease of bone; compressive neuropathies

29

HEREDITARY AND DEGENERATIVE DISORDERS

Storage diseases: Lipidoses, glycogen disorders and leukoenecphalopathies

Gangliosidoses; sphingomyelinoses; cerebrosidoses; mucopolysaccharidoses; mucolipidoses; glycogen storage diseases, leukodystrophies

30

Amino/organic acidopathies, mitochondrial enzyme defects and other metabolic errors

Maple syrup urine disease (MSUD), urea cycle disorders (UCD); propionic acidemia (Pa); methylmalonic acidemia (MMA); deficiency of phenylalanine hydroxylase (Pah); homocystinuria; glutaricaciduria type 1; subacute necrotizing encephalomyelopathy; Alper's disease; myoclonic epilepsy and ragged red fibers; mitochondrial encephalopathy, lactic acidosis and strokelike episodes; fatty acid oxidation disorders; Hartnup's disease; Menkes' disease; porphyrias

31

Chromosomal abnormalities and neurocutaneous disorders

Neurofibromatosis; tuberous sclerosis

32

The degenerative dementias

Progressive aphasia; progressive frontal lobe/frontotemporal syndrome; progressive perceptual motor syndrome; ALS-dementia complex, multiple system atrophy

33

Movement disorders

Multiple system atrophy, stiff-person syndrome

34

Ataxias

Friedreich's ataxia; congenital ataxias; autosomal dominant cerebellar ataxia

35

Degenerative motor, sensory and autonomic disorders

Amyotrophic lateral sclerosis; spinal muscular atrophy; hereditary spastic paraplegias; dystrophinopathies; limb girdle muscular dystrophies; fascioscapulohumeral muscular dystrophy; scapuloperoneal syndrome; myotonic dystrophy; oculopharyngeal muscular dystrophy; Emery-Dreifuss muscular dystrophy; distal myopathies; hereditary sensory and motor neuropathies; hereditary sensory and autonomic neuropathies; Shy-Drager syndrome

36

Inherited muscle, neuromuscular and neuronal disorders

Channelopathies; congenital myopathies; malignant hyperthermia; Brody's disease; congenital myasthenias; familial amyloid polyneuropathy; giant axonal neuropathy; Isaac's disease

37

ACQUIRED METABOLIC AND NUTRITIONAL DISORDERS

Endogenous metabolic disorders

Hypocalcemia; hypercalcemia; hyperthyroidism; hypothyroidism; diabetes

38

Exogenous acquired metabolic disorders of the nervous system: Toxins and illicit drugs

Arsenic; inorganic lead; manganese; inorganic mercury; organic mercury; organophosphate insecticides; organochlorine insecticides; snake and spider venoms; tick paralysis; chickpea (lathyrism); diphtheria; tetanus; botulism, cocaine, amphetamine analogs

39

Nutritional deficiencies and syndromes associated with alcoholism

Thiamine; niacin/nicotinic acid; cobalamin (vitamin B l2 ); pyridoxine (vitamin B6 ); Strachan's syndrome; postgastroplasty polyneuropathy; Marchiafava-Bignami disease; alcoholic myopathy; alcoholic neuropathy

40

INFECTIOUS DISORDERS

Viral infections Nonviral infections

Transmissible spongiform encephalopathies

HIV and AIDS

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