2d:I[856015,["/_next/static/immutable/chunks/1xzisbplk9czp.js","/_next/static/immutable/chunks/3j2i1faptc_-9.js","/_next/static/immutable/chunks/0fma7nlq6immz.js","/_next/static/immutable/chunks/08tq8rmv423j5.js","/_next/static/immutable/chunks/1chr5wkk3j58k.js","/_next/static/immutable/chunks/37kmmh_zm4dov.js","/_next/static/immutable/chunks/311zvdjfxff-f.js","/_next/static/immutable/chunks/1a_hqhrsle_n_.js"],"default"] 2e:T6fa8,

Summary Table

Category	Details
Risk Factors	Age 55 to 75 years, male sex (slight predominance), family history of ALS (5 to 10% familial), military veterans, smoking, prior lead or pesticide exposure
Etiology	Sporadic in 90 to 95% of cases (unknown cause); familial cases linked to SOD1, C9orf72, TDP-43, and FUS gene mutations; glutamate excitotoxicity and oxidative stress are the leading proposed mechanisms
Patient Presentation	Progressive, painless, asymmetric weakness of a limb (most common); difficulty with grip, foot drop, tripping; alternatively presents with dysarthria and dysphagia (bulbar onset)
Classic Physical Exam	Simultaneous upper motor neuron (UMN) and lower motor neuron (LMN) signs in the same patient: hyperreflexia, spasticity, and a positive Babinski (UMN) coexisting with muscle atrophy, fasciculations, and weakness (LMN); tongue fasciculations in bulbar-onset disease; no sensory deficits
Key Diagnostic Results	EMG/nerve conduction studies showing widespread denervation (fibrillation potentials, positive sharp waves, fasciculation potentials) in at least two or more body regions; normal sensory nerve conduction; MRI of brain and spine to exclude structural mimics
Management	Riluzole 50 mg PO twice daily (the classic tested first-line disease-modifying agent); edaravone for slowing functional decline; non-invasive ventilation (BiPAP) when forced vital capacity (FVC) falls below 50%; percutaneous gastrostomy (PEG) for dysphagia; multidisciplinary supportive care
Keywords	"Combined UMN and LMN signs," "fasciculations with hyperreflexia," "progressive weakness without sensory loss," "tongue fasciculations," "split-hand sign," "pseudobulbar affect," "no bowel or bladder involvement"

1. Pathophysiology

ALS is a relentlessly progressive neurodegenerative disease that selectively destroys both upper motor neurons in the motor cortex and lower motor neurons in the brainstem nuclei and spinal cord anterior horn cells. This dual involvement is the defining feature of the disease and the single most important concept tested on exams. No other common condition produces combined UMN and LMN findings in the absence of sensory loss.

Glutamate excitotoxicity is the most widely accepted pathogenic mechanism. Motor neurons are particularly vulnerable to excessive glutamate signaling at NMDA and AMPA receptors. Sustained glutamate stimulation causes intracellular calcium overload, mitochondrial dysfunction, generation of reactive oxygen species, and ultimately neuronal death. This is the rationale for using riluzole, which inhibits presynaptic glutamate release and blocks sodium channels to reduce excitotoxic injury.

In familial ALS (5 to 10% of cases), the two most commonly tested mutations are SOD1 (superoxide dismutase 1), which leads to toxic gain-of-function protein aggregation and oxidative stress, and C9orf72, a hexanucleotide repeat expansion that is the single most common genetic cause of both familial ALS and frontotemporal dementia (FTD). This genetic overlap explains why roughly 15% of ALS patients develop concomitant FTD, presenting with behavioral changes and executive dysfunction alongside motor neuron degeneration.

The reason the patient develops fasciculations, atrophy, and flaccid weakness is straightforward: lower motor neurons die, and denervated muscle fibers begin firing spontaneously (fasciculations) and then waste away (atrophy). The reason the same patient also develops hyperreflexia, spasticity, and a positive Babinski sign is that upper motor neurons, which normally modulate and inhibit spinal reflex arcs, are simultaneously degenerating. The loss of descending inhibitory input "releases" spinal reflexes, producing brisk tendon jerks and extensor plantar responses. This paradox of atrophy (LMN) coexisting with hyperreflexia (UMN) in the same limb is the hallmark finding that clinches the diagnosis.

Sensory neurons, autonomic neurons, and the neurons controlling extraocular muscles and sphincters are characteristically spared. That is why the vignette patient never has numbness, tingling, bladder dysfunction, or eye movement abnormalities. If any of these are present, you must consider an alternative diagnosis.

2. Classification and Clinical Manifestation

Onset Subtypes

Subtype	Frequency	Initial Presentation	Progression Pattern	Prognosis
Limb-onset (spinal)	~65 to 70%	Asymmetric hand weakness (difficulty with buttons, grip) or foot drop and tripping	Spreads contiguously to adjacent myotomes; eventually involves bulbar and respiratory muscles	Median survival 3 to 5 years
Bulbar-onset	~25 to 30%	Dysarthria (slurred, nasal speech), dysphagia, tongue atrophy and fasciculations	Early aspiration risk; limb involvement follows	Median survival 2 to 3 years (worse prognosis)
Respiratory-onset	~3 to 5%	Dyspnea on exertion, orthopnea, morning headache from nocturnal hypoventilation	Earliest need for ventilatory support	Worst prognosis

Revised El Escorial Diagnostic Categories

Category	Criteria
Clinically Definite ALS	UMN + LMN signs in three body regions (bulbar, cervical, thoracic, lumbosacral)
Clinically Probable ALS	UMN + LMN signs in two body regions, with UMN signs rostral (above) to LMN signs
Clinically Probable, Laboratory-Supported	UMN + LMN signs in one region, OR UMN signs alone in one region, with EMG evidence of LMN denervation in at least two limb regions
Clinically Possible ALS	UMN + LMN signs together in one region only, OR UMN signs in two or more regions, OR LMN signs rostral to UMN signs

The Awaji-Shima criteria modified these categories by treating fasciculation potentials on EMG as equivalent to fibrillation potentials and positive sharp waves for evidence of active denervation. This increased diagnostic sensitivity, particularly in bulbar-onset ALS, without sacrificing accuracy.

Clinical Signs by Body Region

Region	UMN Signs	LMN Signs
Bulbar	Spastic dysarthria, brisk jaw jerk, pseudobulbar affect (involuntary laughing or crying)	Tongue atrophy and fasciculations, flaccid dysarthria, dysphagia
Cervical	Upper limb hyperreflexia, spasticity, Hoffmann sign	Hand muscle wasting (thenar, first dorsal interosseous), fasciculations, weakness of grip
Thoracic	Absent superficial abdominal reflexes	Paraspinal muscle denervation on EMG
Lumbosacral	Lower limb hyperreflexia, spasticity, Babinski sign, clonus	Quadriceps and tibialis anterior atrophy, fasciculations, foot drop

A notable exam-relevant sign is the split-hand sign: preferential wasting of the thenar eminence and first dorsal interosseous muscle with relative preservation of the hypothenar muscles. This dissociated pattern of hand wasting is relatively unique to ALS and is frequently described in vignettes.

3. Diagnostic Workup

Test	Role	Key Findings
EMG with nerve conduction studies	Best initial test (after clinical suspicion)	Active and chronic denervation (fibrillation potentials, positive sharp waves, fasciculation potentials) in at least 2 body regions; normal sensory nerve conduction
MRI of brain and spinal cord	Rule out structural mimics	Should be normal or show only subtle corticospinal tract hyperintensity on T2/FLAIR; primarily ordered to exclude cervical myelopathy, tumors, or demyelinating disease
Pulmonary function tests (FVC)	Baseline and ongoing monitoring	FVC below 80% predicted indicates early respiratory compromise; FVC below 50% is the threshold for initiating non-invasive ventilation
Blood tests	Exclude treatable mimics	Creatine kinase (mildly elevated, usually less than 10 times normal), TSH, vitamin B12, serum protein electrophoresis, anti-GM1 antibodies (to rule out multifocal motor neuropathy)
Genetic testing	Familial ALS evaluation	SOD1, C9orf72 repeat expansion; considered when family history is present

There is no single confirmatory "gold standard" test for ALS. The diagnosis is clinical, supported by electrodiagnostic studies and the exclusion of mimics. This is itself a testable concept: if a question asks for the "most accurate test," the answer is the combination of clinical criteria (El Escorial or Awaji) supported by EMG findings, not a single laboratory value.

The first step after clinical suspicion is EMG with nerve conduction studies (NCS). The EMG will demonstrate evidence of active denervation (fibrillation potentials and positive sharp waves) and chronic denervation with reinnervation (large-amplitude, long-duration motor unit potentials and reduced recruitment) across multiple myotomes. Fasciculation potentials are often prominent. The critical finding is that sensory nerve conduction must be normal. If sensory responses are abnormal, the diagnosis is not ALS, and you must consider a polyneuropathy or other condition.

MRI of the brain and the entire spinal cord is ordered not to confirm ALS but to exclude structural lesions that can mimic it. Cervical spondylotic myelopathy is the most common structural mimic: it can produce both UMN signs (from cord compression) and LMN signs (from root compression) in the upper limbs. A clean MRI in a patient with widespread UMN and LMN signs and no sensory deficits strongly supports the diagnosis of ALS.

Bloodwork serves a similar exclusionary purpose. A mildly elevated creatine kinase (typically 1.5 to 3 times the upper limit of normal, rarely exceeding 10 times) is common in ALS due to ongoing muscle fiber breakdown but is non-diagnostic. Thyroid function, B12, and serum protein electrophoresis help rule out metabolic and paraproteinemic neuropathies. Anti-GM1 ganglioside antibodies should be checked because multifocal motor neuropathy with conduction block (MMN) can closely mimic ALS but is treatable with intravenous immunoglobulin.

Pulmonary function testing, particularly the upright and supine FVC, establishes a respiratory baseline. A disproportionate drop in supine FVC suggests diaphragmatic weakness and is an early indicator of respiratory compromise, even when the upright FVC is still relatively preserved.

4. Management and Treatment

Intervention	Indication	Dose and Regimen	Key Notes
Riluzole	Disease modification (prolongs survival)	50 mg PO twice daily, taken on an empty stomach	Extends median survival by approximately 2 to 3 months; monitor LFTs at baseline, monthly for 3 months, then periodically; avoid if baseline ALT exceeds 5 times ULN
Edaravone	Slowing functional decline	60 mg IV daily for 14 consecutive days (cycle 1), then 60 mg IV daily for 10 of 14 days with 14-day drug-free periods (subsequent cycles); oral suspension also available	Most benefit shown in early-stage ALS with preserved respiratory function
Tofersen	SOD1-mutation ALS only	100 mg intrathecal injection, given as 3 loading doses at 14-day intervals, then once every 28 days	First antisense oligonucleotide approved for a genetic subtype of ALS; reduces neurofilament light chain levels
Non-invasive ventilation (BiPAP)	Respiratory support	Initiated when FVC falls below 50% of predicted, or when symptomatic (orthopnea, morning headaches, daytime somnolence)	Single most impactful intervention for prolonging survival and improving quality of life
Percutaneous endoscopic gastrostomy (PEG)	Nutritional support	Placed when oral intake is inadequate or weight loss exceeds 10%, ideally while FVC is still above 50%	Procedure carries higher risk when respiratory function is already severely compromised
Dextromethorphan/quinidine	Pseudobulbar affect	20 mg/10 mg PO twice daily	Treats involuntary laughing or crying; frequently tested as a "next best step" when emotional lability is described
Baclofen or tizanidine	Spasticity	Baclofen 5 mg PO three times daily, titrated up; tizanidine 2 to 4 mg PO three times daily	Symptomatic relief only; avoid oversedation
Multidisciplinary clinic care	Comprehensive support	Ongoing	Neurology, pulmonology, speech therapy, physical therapy, occupational therapy, palliative care, social work

Riluzole is the cornerstone tested answer for disease-modifying therapy in ALS. It works by reducing glutamate-mediated excitotoxicity. Its survival benefit is modest (approximately 2 to 3 months of extended median survival and a higher probability of being alive at 12 months), but it remains the most commonly examined pharmacologic intervention. The most important side effect to know for exams is hepatotoxicity: liver function tests must be monitored, and the drug is contraindicated in patients with baseline transaminases above five times the upper limit of normal.

Edaravone is a free radical scavenger that reduces oxidative stress. It was initially approved based on data showing a slower rate of functional decline in a subset of patients with early ALS and preserved respiratory function ($FVC \geq 80%$ predicted). It is administered intravenously in treatment cycles. An oral formulation became available to reduce the burden of infusion visits. On exams, edaravone is the second disease-modifying agent to know after riluzole.

Tofersen is an antisense oligonucleotide that targets SOD1 mRNA and is approved only for patients with confirmed SOD1 mutations. It is delivered via intrathecal injection. While it reduces cerebrospinal fluid neurofilament light chain (a biomarker of neuronal injury), its clinical benefit on functional outcomes is still being studied. Know that it exists as a genotype-directed therapy, which makes it a potential exam topic when the vignette provides a family history and mentions genetic testing results.

Non-invasive ventilation (NIV) with BiPAP is the single most effective intervention for prolonging survival in ALS, adding 7 to 12 months or more in compliant patients. It is initiated based on symptoms of respiratory insufficiency (orthopnea, morning headaches from CO2 retention, daytime somnolence) or when objective testing shows $FVC < 50%$ predicted, $MIP < -60\ cmH_2O$, or nocturnal oximetry demonstrating desaturation. If a vignette describes a patient with known ALS presenting with morning headaches and daytime fatigue, the next best step is order pulmonary function tests and/or initiate BiPAP, not increase riluzole or add another drug.

PEG tube placement should be performed proactively, ideally while the FVC is still above 50%, because the procedural risk increases with worsening respiratory function. Weight loss exceeding 10% of baseline or recurrent aspiration episodes are strong indications.

End-of-life care is integral. ALS is uniformly fatal, with most patients dying of respiratory failure. Palliative care discussions, advance directive planning, and hospice referral should be addressed early. This is a tested concept: recognizing when the appropriate next step is a goals-of-care discussion rather than another intervention.

5. Differential Diagnosis and Distractors

Differential	Why It Is Similar	Key Discriminator
Cervical spondylotic myelopathy	Can produce UMN signs (cord compression) and LMN signs (nerve root compression) in the upper extremities	Sensory deficits and a dermatomal pain pattern are present; MRI shows cord compression at the cervical level; symptoms are confined to the cervical distribution, not widespread
Multifocal motor neuropathy (MMN)	Pure LMN weakness, often asymmetric and starting in the hands, with fasciculations	No UMN signs; NCS shows conduction block; positive anti-GM1 antibodies; responds to intravenous immunoglobulin (treatable)
Primary lateral sclerosis (PLS)	Progressive spasticity, hyperreflexia, and Babinski signs	Pure UMN involvement with no LMN signs (no fasciculations, no atrophy on EMG); much slower progression; survival measured in decades
Spinal muscular atrophy (SMA)	Proximal weakness, muscle atrophy, fasciculations (LMN disease)	Pure LMN disease with no UMN signs; symmetric and proximal; onset typically in childhood or adolescence; caused by SMN1 gene deletion
Myasthenia gravis	Bulbar symptoms (dysarthria, dysphagia), limb weakness	Fatigable weakness that worsens with repetitive use and improves with rest; no fasciculations or atrophy early on; positive anti-AChR or anti-MuSK antibodies; decremental response on repetitive nerve stimulation
Kennedy disease (SBMA)	Adult male with progressive LMN weakness, fasciculations (including tongue), bulbar symptoms	X-linked recessive (CAG trinucleotide repeat in androgen receptor gene); gynecomastia and testicular atrophy are present; sensory neuropathy on NCS; much slower progression
Inclusion body myositis (IBM)	Progressive weakness of grip and quadriceps in older adults	Weakness is proximal AND distal but follows a myopathic pattern (elevated CK, myopathic EMG changes); finger flexor and quadricep weakness is characteristic; muscle biopsy shows rimmed vacuoles
Multiple sclerosis	Can have UMN signs, spasticity, and Babinski	Sensory symptoms, visual changes (optic neuritis), and bladder dysfunction are present; relapsing-remitting course; MRI shows periventricular demyelinating lesions

6. Traps and High-Yield Pearls

The single most common way students get ALS questions wrong is by failing to recognize that UMN and LMN signs must coexist in the same patient without sensory involvement. When a vignette describes fasciculations, atrophy, and weakness (LMN features) alongside hyperreflexia, spasticity, and a Babinski sign (UMN features), and explicitly states that sensation is intact, the diagnosis is ALS. Students who focus only on the LMN findings may select a peripheral neuropathy or motor neuron disease variant like spinal muscular atrophy. Students who focus only on the UMN findings may select multiple sclerosis or a myelopathy. The tested competency is the ability to synthesize both sets of findings and recognize that their simultaneous presence, in the absence of sensory loss, narrows the diagnosis to ALS.

A second common trap involves the bulbar-onset presentation. A vignette may describe an older adult with progressive slurred speech, difficulty swallowing, and tongue wasting. Students may gravitate toward myasthenia gravis. The discriminator is that myasthenia gravis produces fatigable weakness (worse at end of day, better after rest) and does not cause fasciculations or muscle atrophy early in the course. ALS bulbar symptoms are progressive and non-fatigable, and tongue fasciculations are a strong clue.

Third, students are often tested on the next best step when respiratory symptoms appear. A patient with known ALS presenting with orthopnea and morning headaches is describing early respiratory failure due to diaphragmatic weakness. The answer is not intubation (which raises end-of-life considerations) and not a new medication. The answer is pulmonary function testing (FVC) and initiation of non-invasive ventilation (BiPAP).

Finally, know that riluzole is the tested pharmacologic answer for disease-modifying therapy. It does not reverse symptoms or dramatically extend life, but it is the first-line agent that exam-writers expect you to select. Do not confuse it with rivastigmine (used for Alzheimer disease) or rizatriptan (used for migraine). The mechanism (glutamate inhibition) and the required monitoring (liver function tests) are both testable.

The core competency being assessed across ALS questions is pattern recognition: identifying the combination of upper and lower motor neuron degeneration, confirming the absence of sensory and autonomic involvement, selecting the correct electrodiagnostic study (EMG/NCS), and knowing the stepwise management from riluzole initiation through respiratory support with BiPAP.

1e:["$","$L2d",null,{"article":{"id":"d885899a-18e9-4ee8-82e3-6ea8be1023f3","title":"Amyotrophic Lateral Sclerosis (ALS)","content":"$2e","category":"Neurologi","created_at":"2026-07-18T07:58:28.398704+00:00","status":"published","subcategory":null},"questionCount":0,"sections":[{"id":"section-pathophysiology","num":"01","title":"Pathophysiology"},{"id":"section-classification-and-clinical-manifestation","num":"02","title":"Classification and Clinical Manifestation"},{"id":"section-diagnostic-workup","num":"03","title":"Diagnostic Workup"},{"id":"section-management-and-treatment","num":"04","title":"Management and Treatment"},{"id":"section-differential-diagnosis-and-distractors","num":"05","title":"Differential Diagnosis and Distractors"},{"id":"section-traps-and-high-yield-pearls","num":"06","title":"Traps and High-Yield Pearls"}],"hasSummaryTable":true}]