Case Presentation: A 75 year-old man with history of type II diabetes and hypertension presented with progressive dyspnea. Two weeks prior, he had presented with similar symptoms that were attributed to COPD due to a remote history of smoking. He was hypoxic upon presentation requiring bi-level positive pressure ventilation with a FiO2 of 40%. He was admitted for respiratory failure.
On physical exam, breath sounds were diminished at the lung bases, without wheezing or rales. Motor exam showed fatigable weakness of the proximal limb muscles, deltoid and quadriceps atrophy, scattered fasciculations, brisk reflexes diffusely, postural tremor, and bilateral extensor plantar reflexes.
Venous blood gas revealed pH 7.27, PCO2 101, PO2 25, and HCO3 46.1. Chest X-ray revealed low lung volumes, heightened hemi-diaphragms, and bibasilar atelectasis. CT ruled out pulmonary embolism, but showed a right lower lobe infiltrate.
Patient was started on antibiotics for aspiration pneumonia and also treated for a COPD exacerbation with steroids and nebulizer treatments. He showed little respiratory improvement. Given his neurologic findings, elevated hemi-diaphragms, and marked hypercarbia, a negative inspiratory force was measured to look for neuromuscular weakness. It was indeed diminished. Patient underwent EMG testing which was consistent with myasthenia gravis (MG), although serologic testing was negative.
Patient showed improvement with treatment for MG with pyridostigmine and prednisone, and was discharged home. He was readmitted with worsening dyspnea two months later. Exam showed diffuse fasciculations and hyperreflexia. Repeat EMG showed fibrillations consistent with amyotrophic lateral sclerosis (ALS). Patient was started on riluzole and referred to palliative care
Discussion: Neurologic disorders such as myasthenia gravis and ALS can frequently result in respiratory weakness. However, they rarely present initially with purely respiratory symptoms. In this case, the patient was initially diagnosed with COPD and later pneumonia as the etiology of his respiratory issues, despite the fact that his presentation did not clearly fit these etiologies (patient was a remote smoker with no history of COPD, there were no emphysematous changes on imaging, exam did not reveal wheezing, and his hypoxia/hypercarbia were out of proportion to the minor pneumonia found on imaging). In addition, he displayed signs consistent with an underlying neurologic disorder, including muscle atrophy, fasciculations, hyperreflexia, as well as signs specific for respiratory muscle weakness including elevated hemi-diaphragms on imaging, hypercarbia, and a decreased negative inspiratory force.
Conclusions: Acute respiratory failure has a multitude of causes. Rarely, it can be the initial manifestation of neurologic disease. As in this case, a careful examination of the evidence including a detailed neurologic exam can help reveal clues that point to an underlying neurologic illness.