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Introduction

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A 60-year-old man with a history of hypertension is admitted with several days of fever and generalized weakness. He complains of diplopia and anorexia and is found to have a low-grade fever of 100.1°F. Over the next few days he clinically deteriorates, developing progressive encephalopathy, worsening right arm weakness, bulbar weakness, and an inability to walk. A head computed tomography (CT) shows nonspecific white matter changes. He is intubated for airway protection and transferred to the neurologic intensive care unit (NICU). On presentation, his examination shows vital signs: temperature 100.2°F, HR 90 bpm, BP 130/90 mm Hg. He has intact cranial nerves except for an absent gag reflex. Motor examination reveals increased tone throughout, extensor posturing of the left arm, flexor posturing of the right arm, and no response in the lower extremities.

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What is the differential diagnosis for this patient? And what are the essential next steps?

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The constellation of fever, generalized weakness, and bulbar dysfunction can be from a multitude of diseases. Grouping them according to location of disease is useful in guiding diagnostic tests that are needed. Infectious etiologies for central nervous system (CNS) dysfunction (ie, meningitis, encephalitis, cerebral abscess) are important to diagnose and treat quickly. Given the emergent necessity of treating infectious etiologies of meningitis and/or encephalitis, it is prudent to begin treatment with antiviral and antibacterial agents while diagnostic testing proceeds. Intravenous acyclovir should be strongly considered as well as intravenous medication to treat bacterial meningitis, tuberculosis, and fungal infections, depending on clinical suspicion. Diagnosis and treatment of infectious diseases will be discussed in Chapter 7. To diagnose CNS infection, a lumbar puncture should not be delayed.

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Although unlikely in this case, perhaps the most time-sensitive diagnosis would be a vascular etiology. In a patient with vascular risk factors and cranial nerve signs/symptoms, a posterior circulation ischemic event is most important to diagnose quickly. Although a noncontrast head CT is effective in diagnosing intracerebral hemorrhages, in this setting it is probably not very helpful. Magnetic resonance imaging (MRI) of the brain is the most effective tool for diagnosing ischemic strokes and also will help in diagnosing other diseases.

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Once infectious and vascular etiologies are addressed, one must consider inflammatory diseases. The history of symptoms occurring after a viral prodrome, malaise, and low-grade fever is suggestive of a postinfectious inflammatory process. Acute disseminated encephalomyelitis (ADEM) is a disease that can cause rapid mental status changes and multifocal neurologic deficits. An MRI with and without gadolinium is necessary to diagnose ADEM.

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Other possible parenchymal diseases include metastatic disease, other autoimmune inflammatory diseases such as tumefactive multiple sclerosis (MS), and CNS manifestations of systemic autoimmune diseases: lupus, Behçet syndrome, vasculitis, and paraneoplastic diseases.

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Leptomeningeal processes can cause encephalopathy and multifocal neurologic symptoms. Again, infectious processes are the most urgent to diagnose. Other possibilities are inflammatory diseases such as sarcoid, ...

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