Diagnostic Tests for Spinal Muscular Atrophy
Spinal Muscular Atrophy Tests: Book Excerpts
Spinal Muscular Atrophy Diagnosis: Book Excerpts
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MUSCULAR ATROPHY:
DIAGNOSTIC WORKUP
(Algorithmic Diagnosis of Symptoms and Signs)
The basic workup includes a CBC, sedimentation rate, urinalysis, chemistry panel, ANA titer, serum protein electrophoresis, and VDRL test. Additional muscle enzymes may be ordered such as serum aldolase and CPK. A 24-hr urine collection for creatinine and creatine may be done.
At this point, it is best to consult a neurologist. He will probably order nerve conduction velocity studies and EMGs of the involved extremities. He also will be best qualified to determine the need for CT scans or MRIs of the brain or spine, as well as the particular study to order in each individual case. At times, spinal fluid analysis and muscle biopsies may be necessary to solve the problem. Also, a Tensilon test or acetylcholine receptor antibody titer may be ordered in suspected myasthenia gravis.
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Source: Algorithmic Diagnosis of Symptoms and Signs, 2003
Alteration in Consciousness:
Diagnostic Approach
(The Diagnostic Approach to Symptoms and Signs in Pediatrics)
When individualpresents with alteration of consciousness, diagnosis and treatment mustproceed concurrently, not serially.ABCs of resuscitation (airway, breathing,circulation) take precedence over other diagnostic and therapeuticmeasures. Airway must be cleared, and oxygen should be given bymask and bag ventilation.Failure of adequate ventilation requiresintubation.Hypotension or shock should be treatedwith volume expansion.With suspected or known head or necktrauma, head should be stabilized until lateral cervical spine radiographcan be performed to determine whether cervical spine injury hasoccurred.Level of consciousness and responsiveness,motor function, pupil size and responses, and extraocular movementsshould be evaluated. Presence or absence of meningeal signs as wellas focal hemispheric or brainstem findings also should be noted.Unless diagnosis has been establishedby history and physical exam, a number of tests need to be performed.Measurementof blood glucose should be done immediately at bedside.Blood should be sent for CBC with differential;serum electrolytes, glucose, creatinine, calcium, magnesium, ammonia;blood urea nitrogen; liver function tests; blood culture; and toxicology screen.Urine should be obtained for UA, urineculture, and toxicology screen. Vital Signs
Respiratory Rate and Pattern
Dyspneaand/or tachypnea may occur with pneumonia, any cause ofmetabolic acidosis, and lesions of lower midbrain–upperpontine tegmentum.Slow, irregular respirations may beassociated with drug intoxication, septicemia, and intracranialmass lesion. With acute head injury or diffuse brain damage of anycause, abnormal breathing patterns often overlap, making it difficultto relate specific pattern with discrete location of brain damage. Heart Rate
Bradycardia,if associated with hypertension and periodic breathing, suggestsincreased intracranial pressure.Tachycardia may occur with hypovolemicshock (dehydration, blood loss, diabetic ketoacidosis) and anticholinergicpoisoning. Blood Pressure
Hypertensionmay occur with increased intracranial pressure and with drug overdoses (amphetamines,cocaine, phencyclidine).Hypotension may occur with hypovolemia(fluid losses from gastroenteritis, acute blood loss, diabetic ketoacidosis),septicemia, adrenal insufficiency, and ingestion of alcohol or barbiturates. Temperature
Hyperpyrexiamay indicate presence of infection (bacterial meningitis, septicemia, pneumonia),heat stroke, or cocaine overdose. Although uncommon, brain lesionthat has disturbed temperature-regulating center also may producehyperpyrexia.Hypothermia may occur with severe hypovolemiaas well as with barbiturate or alcohol ingestion. Level of Consciousness and Responsiveness
Level ofconsciousness can be determined by noting degree of arousability.Response to name, simple commands,or painful stimuli (sternal pressure or pinching side of neck, innerarm, or thigh) can be used to evaluate degree of unresponsiveness.Eye opening or any form of speakingincluding grunting or groaning suggests some degree of functionof reticular activating system.Speech and purposeful withdrawal orlocalization of painful stimuli are signs of intact cortical function. Motor Function
Restlessmovements of arms and legs, variable resistance to passive movement,complex avoidance movements, and discrete protective movements generallyindicate intact corticospinal tracts, whereas asymmetry of functionmay indicate hemiparesis.Presence of posturing should be noted.Decorticate posturing consists of flexion of arms, wrists, and fingerswith adduction of upper extremities, and extension, internal rotation,and plantar flexion of lower extremities. Associated with diffusedamage to cerebral cortex and subcortical white matter or basalganglia. Decerebrate posturing, which consists of arm and hand extensionand back arching, is associated with extensive midbrain damage.Flaccid extremities and absence ofany motor response indicate further depression of brainstem function. Pupil Size and Responses
Exam ofpupils and their reactivity help determine level and location oflesions affecting reticular activating system in brainstem. Anyreactivity signifies intact parasympathetic and sympathetic pathwaysof oculomotor nerve. Bilateral lesions of midbrain that interruptthis pathway produce dilated unreactive pupils. Pontine lesionsproduce miotic pupils with only mild reaction to light. Unilateral pupillarydilatation suggests third nerve compression and impending uncalherniation.Generally, pupils remain reactive withmetabolic or toxic causes of coma. Exceptions include atropine orscopolamine poisoning, which causes dilated unreactive pupils; glutethimidepoisoning, which may cause medium to large unreactive pupils; opiatepoisoning (morphine, heroin), which causes pinpoint pupils withonly slight constriction to light; and severe anoxia with cardiacarrest, which produces fixed and dilated pupils. Miosis is usuallyseen with opiate, organophosphate, or clonidine overdosage, whereasmydriasis is usually seen with anticholinergic poisoning (tricyclicantidepressants) or with stimulant overdosage (amphetamines, cocaine). Extraocular Movements
Evaluationof eyes at rest, abnormal spontaneous eye movements, and ocularresponse to labyrinthine function provide important informationin assessment of alteration of consciousness.Cerebral lesions (usually frontal lobe)usually produce conjugate deviation of eyes to side of lesion andnormal labyrinthine responses, whereas unilateral pontine lesionsusually produce eye deviation away from side of lesion as well asabnormal labyrinthine responses. Midbrain lesions that involve oculomotornucleus or nerve or pontine lesions involving abducens nucleus ornerve may cause abduction of ipsilateral eye.Ocular response to vestibular stimulationalso helps evaluate integrity of brainstem function in childrenwith alteration of consciousness. Brainstem function is intact whenice water injection of 50 mL into external auditory canal with headflexed to 30 degrees produces conjugate horizontal eye deviationto side of injection and horizontal rapid nystagmus to oppositeside. Absence of such reflexes indicates severe brainstem dysfunction.Oculocephalic (doll's eye)reflex is also used to produce vestibular stimulation, but it iscontraindicated with suspected cervical spine injury. Head is rotatedfrom side to side and positive response indicating intact brainstemfunction is conjugate horizontal eye movement in opposite directionfrom head turn. Further Evaluation and Specific Diagnosis
Vital signsand assessments already described usually indicate whether any focal hemisphericor brainstem dysfunction exists. Final task is to make definitivediagnosis.Focal neurologic signs including asymmetricmovements and abnormal postures usually signify structural lesionin cerebral hemisphere, which also may affect brainstem function.Lesions above tentorium may cause alterationof consciousness by depression of large portions of both cerebralhemispheres, whereas lesions below tentorium (usually tumor or collectionof blood in posterior fossa) depress consciousness by compressionof brainstem structures.Presence of increased intracranialpressure may lead to central or uncal cerebral herniation. Centralherniation refers to rostrocaudal pattern of deterioration withloss of consciousness and irregular respirations followed by bilateraldilated unresponsive pupils and either decorticate or decerebrateposturing. Uncal herniation occurs more suddenly with loss of consciousnessand unilateral dilated pupil occurring almost simultaneously.Hemiparesis or hemiplegia may occurcontralateral to lesion.In cases of suspected structural lesion ± historyof head trauma, CT should be performed immediately. When herniationor impending herniation is suspected, patient should be intubated,hyperventilated, and given mannitol to acutely decrease increasedintracranial pressure prior to CT.Meningeal signs (stiff neck, Kernigor Brudzinski signs) commonly occur with bacterial meningitis andsubarachnoid hemorrhage. Lumbar puncture should be performed withsuspected bacterial meningitis or viral encephalitis. CT shouldbe performed first to rule out mass lesion in individuals with focalneurologic signs or symptoms of coma. If patient is unstable, appropriateantibiotic therapy should be given for suspected bacterial meningitisafter blood culture has been drawn, and lumbar puncture may be deferreduntil child is stable. In individuals with suspected subarachnoidhemorrhage and increased intracranial pressure, CT should be performedimmediately.Individuals without meningeal or focalneurologic signs may have head injury, drug intoxication, seizure,or metabolic disorder. Precise drug history is important but oftenis unavailable. 3 specific antidotes are available:Naloxone foropiate overdosePhysostigmine for anticholinergic poisoningFlumazenil for benzodiazepine overdose Metabolic causes of coma tend to producesymmetric hemispheric responses with normal brainstem function.With hyperammonemia in neonatal period,urea cycle defects and organic acid disorders should be suspected. Fig.3.1 (Adapted from Batshaw ML. Inborn errors of ureasynthesis. Ann Neurol 1994;35:137, with permission.) provides schemeto determine cause of hyperammonemia in neonates. Measurement ofserum ammonia, amino acids, lactate, and pyruvate, as well as urinaryorganic acids and orotic acid, will identify virtually all of geneticcauses of hyperammonia in this age group. Plasma acylcarnitine profilecan help diagnose various fatty acid oxidation defects. In a fewinstances (carbamyl phosphate synthetase and N-acetylglutamate synthetasedeficiencies), specific enzyme analysis must be performed to confirmdiagnosis. In infantsand children with hyperammonemia, scheme used for neonates can befollowed. However, if urinary organic acids are normal, prothrombintime and serum bilirubin should be measured. If these results areabnormal, liver disease, drugs, hepatotoxins, and Reye syndromeshould be considered. Also, if plasma citrulline is normal, plasmaarginine should be measured. Increase in plasma arginine signifiesarginase deficiency. Low or normal plasma arginine suggests 2 possibilities:lysine protein intolerance or hyperornithinemia-hyperammonemia-homocitrullinemiasyndrome. Increase in urinary lysine signifies lysine protein intolerance,whereas increase in plasma ornithine and urinary homocitrulline signifieshyperornithinemia-hyperammonemia-homocitrullinemia syndrome. Otherinvestigations depend on clinical findings and results of abovetests.
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Source: The Diagnostic Approach to Symptoms and Signs in Pediatrics, 2006
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