A 71-year-old man was transferred to the medical intensive care unit (MICU) from another facility for weaning from mechanical ventilation. The original presenting symptoms were constitutional (fatigue, malaise, and a 15-lb weight loss) and neurologic (dizziness, syncope, and progressive weakness).
The history revealed a condition that had become progressively worse over 3 to 4 weeks, predominated by cognitive impairment, mood swings, somnolence, and limb weakness. No respiratory symptoms were noted.
On admission to the MICU, the patient was somnolent and comfortable. Examination of the lungs and heart was normal. Cranial nerve function was intact but rotatory nystagmus was noted. Muscle tone was decreased globally; power was reduced significantly in the arms and legs, and tendon reflexes were absent and sensation diminished in the legs. It was difficult to ascertain sensory level. Fatigability was not elicited with ocular muscles or handgrip.
Chest films obtained at the primary medical facility showed a mass in the right lung field (Figure). MRI and CT scans of the head had found no abnormalities. CT scan of the chest revealed an incidental mediastinal mass. Bronchoscopic biopsy revealed limited-stage small-cell lung cancer (SCLC).
At the referring facility, the patient received one cycle of chemotherapy with cisplatin and etoposide. During the stay he appeared extremely lethargic and sleepy, symptoms not thought to be treatment-related. Examination found numbness and parasthesia in the hands and feet and hand tremors. The patient experienced a generalized tonic-clonic seizure during which he was intubated. When extubated, he experienced acute hypercapnic respiratory failure, was placed back on ventilation, and was transferred for management.
Difficulty in weaning this patient from mechanical ventilation was one feature of a failing neurologic state that included altered sensorium, somnolence, seizure, and signs of peripheral neuropathy—ventilatory failure and lower motor neuron disease.
MRI and CT imaging of the brain found no structural etiology. Electromyography showed diffuse sensory and motor axonal degeneration. Assays of serum and cerebrospinal fluid (CSF) were found mildly positive for anti-Hu antibody.
What is causing the patient’s neurologic weakness?
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