A 12-year-old boy is brought to the emergency department by his parents as "he cannot walk anymore." The patient has had a pins-and-needles sensation and weakness in both feet for the past few days. This morning, he could not stand or move his legs and has bilateral thigh pain. Two weeks ago, the patient had a febrile diarrheal illness that resolved on its own. He has had no headaches, nausea, vomiting, or recurrent diarrhea. He and his family are vegetarians, and they recently visited a petting zoo. The patient has no significant past medical history, and vaccinations are up to date. On arrival, temperature is 36.7 C (98.1 F), blood pressure is 150/90 mm Hg, pulse is 92/min, and respirations are 16/min; pulse oximetry is 99% on room air. Physical examination shows symmetric flaccid paralysis of the lower extremities and absent ankle and patellar deep tendon reflexes. Sensation is intact to light touch in both legs. The upper extremities are weak and hyporeflexic. There is no photophobia or nuchal rigidity. Which of the following structures is primarily impaired in this patient's condition?

Question

A 12-year-old boy is brought to the emergency department by his parents as "he cannot walk anymore."  The patient has had a pins-and-needles sensation and weakness in both feet for the past few days.  This morning, he could not stand or move his legs and has bilateral thigh pain.  Two weeks ago, the patient had a febrile diarrheal illness that resolved on its own.  He has had no headaches, nausea, vomiting, or recurrent diarrhea.  He and his family are vegetarians, and they recently visited a petting zoo.  The patient has no significant past medical history, and vaccinations are up to date.  On arrival, temperature is 36.7 C (98.1 F), blood pressure is 150/90 mm Hg, pulse is 92/min, and respirations are 16/min; pulse oximetry is 99% on room air.  Physical examination shows symmetric flaccid paralysis of the lower extremities and absent ankle and patellar deep tendon reflexes.  Sensation is intact to light touch in both legs.  The upper extremities are weak and hyporeflexic.  There is no photophobia or nuchal rigidity.  Which of the following structures is primarily impaired in this patient's condition?

Quizplus · Accepted Answer

11ec25c8_d5a6_11e7_bc81_65fc65b9d388_MD0003_00 Guillain-Barré syndrome is an immune-mediated polyneuropathy caused by demyelination of peripheral nerve fibers. Most patients have a preceding respiratory or gastrointestinal infection, likely Campylobacter in this patient with recent direct contact with animals, that triggers an initial immune response. These antibodies are then redirected toward cross-reacting antigens on myelin or axons, a process known as molecular mimicry. Motor nerves are most commonly affected, but sensory and autonomic nerves may also be involved. Presentation includes ascending weakness, often accompanied by paresthesias and neuropathic pain, as seen in this patient. Weakness begins in the lower extremities and ascends to involve the respiratory and bulbar muscles. The most severe symptoms include flaccid paralysis with diminished or absent deep tendon reflexes and respiratory failure. Accompanying autonomic symptoms (eg, blood pressure/heart rate instability, ileus) often parallel the severity of motor deficits. Treatment includes intravenous immunoglobulin or plasmapheresis, and most children fully recover. (Choice A) Illnesses that involve the anterior horn cells include spinal muscular atrophy (typically a flaccid paralysis in infancy), poliomyelitis (unlikely in a vaccinated patient), and amyotrophic lateral sclerosis (upper and lower motor neuron disease in adults). This patient's age and vaccination status make these conditions unlikely. (Choice B) Vegetarians and vegans are at increased risk of vitamin B₁₂ deficiency, which can cause subacute degeneration of the dorsal and lateral spinal columns (ie, upper motor neurons), leading to weakness and paresthesias. However, ataxia and loss of vibration and position sense are typically also present but are not seen in this patient. (Choice C) Myopathies, or disorders involving muscle fibers (eg, polymyositis, dermatomyositis), typically cause proximal muscle weakness without paresthesias or areflexia, both of which are seen in this patient. (Choice D) Diseases of the neuromuscular junction include botulism (descending flaccid paralysis), myasthenia gravis (weakness that worsens with use and improves with rest), Lambert-Eaton syndrome (progressive proximal muscle weakness), and organophosphate poisoning (weakness accompanied by multisystem cholinergic symptoms). Educational objective: Guillain-Barré syndrome typically presents with ascending weakness and diminished/absent deep tendon reflexes following a recent gastrointestinal or respiratory infection. The pathogenesis of this syndrome is the immune-mediated demyelination of peripheral nerve fibers. References: Guillain-Barré syndrome. (http://www.ncbi.nlm.nih.gov/pubmed/23418763) Guillain-Barré syndrome. (http://www.ncbi.nlm.nih.gov/pubmed/22081202)

A 12-Year-Old Boy Is Brought to the Emergency Department by His