Clinical Reasoning: A 35-Year-Old Patient With Rapidly Progressive Ascending Weakness Leading to Loss of Brainstem Reflexes

A 35-year-old previously healthy patient presented to an outside hospital emergency department with low back pain, myalgias, arthralgias, and shortness of breath.The only pertinent medical history included routine vaccinations (tetanus, diphtheria and pertussis, inactivated poliovirus, hepatitis B, varicella, and COVID-19) administered 5 days before presentation.There was no reported history of animal bite or scratch.Examination was documented with preserved strength and reflexes.Lumbar spine x-ray was unremarkable, and the patient was discharged with nonsteroidal anti-inflammatory medications.Three days later, the patient represented to the same hospital with progressive bilateral leg weakness and rhabdomyolysis, with serum creatinine kinase of 15,000 units per liter.On examination, the patient was with 4+/5 strength in his bilateral upper extremities, 1/5 in bilateral hip flexion, and 2/5 in bilateral knee extension/flexion and plantarflexion/dorsiflexion.He was noted to have 1+ patellar reflexes bilaterally, which progressed to absent reflexes throughout the following day.Cranial nerve testing was normal.No significant sensory loss was documented.The examiner noted "bizarre behaviors" including paranoia and holding blankets over his face, and speech therapists documented odynophagia.Other clinicians documented refusal of oral intake and intravenous fluids with frequent spitting and tachypnea. Questions for Consideration:1.Where does this process localize?2. How does this patient's presentation and history inform the differential diagnosis?3. What diagnostic testing would you recommend for this patient?