Amyotrophic Lateral Sclerosis (ALS) for USMLE Step 2 & COMLEX-USA Level 2

Amyotrophic Lateral Sclerosis (ALS) for the USMLE Step 2 & COMLEX-USA Level 2 focuses more on the clinical presentation, diagnosis, and management of the disease. Clinical Presentation

• Initial Symptoms: Progressive, asymmetric weakness. May start in the hands or legs (limb-onset) or present with dysarthria and dysphagia (bulbar-onset).
• UMN signs: Spasticity, hyperreflexia, and the Babinski sign.
• LMN signs: Muscle atrophy, fasciculations, and flaccid paralysis.
• Bulbar Involvement: Dysphagia, dysarthria, tongue atrophy, and difficulty chewing/swallowing.
• Respiratory Involvement: Dyspnea due to diaphragmatic weakness can occur later, often leading to respiratory failure.

Differential Diagnosis

• Multiple Sclerosis (MS): Consider MS in younger patients with UMN signs but differentiate based on sensory findings and brain lesions on MRI.
• Cervical Spondylosis: Can mimic ALS with UMN and LMN signs; MRI can help differentiate by showing cord compression.

Diagnosis

• Clinical Diagnosis based on UMN and LMN signs in at least three body regions.
• Electromyography (EMG): Shows widespread denervation and reinnervation, confirming LMN degeneration.
• Nerve Conduction Studies (NCS): Normal sensory responses help differentiate ALS from peripheral neuropathies.
• MRI of Brain/Spine: Done to rule out structural causes (like cervical spondylosis or tumors).

Key Diagnostic Criteria (El Escorial Criteria)

• Must demonstrate UMN and LMN signs in multiple regions of the body.

Management

• Riluzole: First-line treatment, slows progression by reducing glutamate excitotoxicity.
• Edaravone: Antioxidant therapy that may slow functional decline in some patients.
• Symptomatic Management:
• Spasticity: Baclofen or tizanidine.
• Sialorrhea: Atropine or glycopyrrolate.
• Dysphagia: Gastrostomy may be necessary for feeding.
• Respiratory support: Non-invasive ventilation (BiPAP) or invasive mechanical ventilation in advanced stages.

Prognosis

• ALS is progressive and usually fatal within 3–5 years due to respiratory failure.
• Bulbar-onset ALS tends to have a worse prognosis than limb-onset ALS.

Interdisciplinary Care

• Multidisciplinary care involving neurologists, pulmonologists, physical therapists, speech therapists, and palliative care specialists to improve quality of life.

For Step 2, focus is more on clinical management and diagnosis, with an emphasis on distinguishing ALS from other neurologic disorders and managing symptoms to improve patient quality of life.