Educational objective: Bacterial meningitis causes an increase in cerebrospinal fluid (CSF) neutrophil count and protein concentration as well as a decrease in CSF glucose. Streptococcus pneumoniae is a leading cause of community-acquired pneumonia, otitis media, and meningitis in adults. S pneumoniae appears on Gram stain as lancet-shaped, Gram-positive cocci in pairs.

A 68-year-old woman is brought to the emergency department due to confusion and lower extremity weakness. The symptoms began 2 days ago along with fever, headache, malaise, and myalgias. Today, the patient was noted to be confused and had difficulty ambulating due to left lower extremity weakness. The patient has a history of lymphoma in remission, hypertension, and type 2 diabetes mellitus. She drinks alcohol socially but does not use tobacco or illicit drugs. She is visiting her family in Texas for the summer and has never traveled outside the United States. Temperature is 38.3 C (101 F), blood pressure is 130170 mm Hg, and pulse is 96/min. The patient is oriented to place and person only and has a coarse hand tremor. There is flaccid paralysis of the left lower extremity with preserved sensation. CT scan of the head shows no abnormalities. Lumbar puncture is performed, and cerebrospinal fluid analysis shows lymphocytic pleocytosis and elevated protein. Cerebrospinal fluid polymerase chain reaction testing yields viral RNA.

Educational objective: West Nile virus is a single-strand flavivirus transmitted by mosquitoes, most commonly in the summer. Most infections are asymptomatic or may present with a flu-like illness (West Nile fever), often with a maculopapular or morbilliform rash. Neuroinvasive disease manifests as meningitis, encephalitis, or asymmetric flaccid paralysis; patients may have parkinsonian features.

A 35-year-old, right-handed mechanic comes to the clinic due to progressive right hand weakness. The patient frequently uses a screwdriver at work. Neurologic examination shows preserved sensation in the upper limbs. There is weakness on extension of the fingers and thumb in the right hand. Strength is otherwise intact. Triceps reflexes are 2+ and bilaterally symmetric.

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Educational objective: Injury to the radial nerve at the supinator muscle may occur due to repetitive pronation/supination of the forearm, direct trauma, or subluxation of the radius. Patients typically have weakness during finger and thumb extension (ie, finger-drop) without wrist drop or sensory deficits.

A 23-year-old man comes to the physician at his girlfriend's insistence. She says that the patient's frequent snoring keeps her up at night and that in the last 4 months he has twice fallen asleep while they were talking. In this same period, the patient says that he has regularly fallen asleep in the afternoon while reading or watching television but typically feels refreshed after a brief nap. When asked whether he experiences any other symptoms, the patient hesitantly reveals that he sometimes hears a voice call his name prior to falling asleep. He also reports uncharacteristic episodes of clumsiness in which he has suddenly dropped objects or fallen to his knees. Examination shows no abnormalities.

Educational objective: Narcolepsy is a chronic sleep disorder characterized by excessive daytime sleepiness, cataplexy, and REM sleep-related phenomena (ie, hypnagogic/hypnopompic hallucinations, sleep paralysis).

A 21-year-old woman comes to the office due to a long history of episodic headaches, dizziness, and gait imbalance. The headaches are located in the occipital region, are characterized as dull, and last for several hours. Physical examination reveals gait ataxia but no focal weakness or sensory loss. MRI of the brain shows low-lying cerebellar tonsils extending below the plane of the foramen magnum into the vertebral canal.

Educational objective: Chiari malformations are congenital disorders that result from underdevelopment of the posterior fossa, causing parts of the cerebellum and medulla to herniate through the foramen magnum. Chiari type I is relatively benign and presents during adulthood with occipital headache and cerebellar dysfunction. Chiari type II is a more severe form that affects neonates and is often associated with lumbar myelomeningocele and hydrocephalus.

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Educational Objective: Symmetrical enlargement of the ventriculi is characteristic of communicating hydrocephalus. Communicating hydrocephalus usually occurs secondary to dysfunction or obliteration of subarachnoid villi. This dysfunction is usually a sequelae of meningeal infection (including tuberculosis meningitis) or subarachnoid/intraventricular hemorrhage.