Differentials

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

No differentiating signs and symptoms.

INVESTIGATIONS

Cerebrospinal fluid (CSF) polymerase chain reaction (PCR): positive for herpes simplex virus RNA.

MRI/CT head: shows focal temporal lobe abnormalities.

Electroencephalogram: periodic lateralizing epileptiform discharges.[58][59]

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

No differentiating signs and symptoms.

INVESTIGATIONS

Serology: 4-fold increase in virus antibody titer between acute and convalescent serum; detectable IgM antibodies to virus in a single serum or cerebrospinal fluid (CSF) sample. Plaque reduction neutralization test (PRNT) can delineate West Nile virus from other zoonoform viral infections.

Virus isolation: virus can be isolated from tissue, blood, or CSF.[60][61]

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

No differentiating signs and symptoms.

INVESTIGATIONS

Serology: 4-fold increase in virus antibody titer between acute and convalescent serum; detectable IgM antibodies to virus in a single serum or CSF sample.

Virus isolation: virus can be isolated from tissue, blood, or CSF.[61]

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

No differentiating signs and symptoms.

INVESTIGATIONS

Serology: 4-fold increase in virus antibody titer between acute and convalescent serum; detectable IgM antibodies to virus in a single serum or CSF sample.

Virus isolation: virus can be isolated from tissue, blood, or CSF.[61]

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

No differentiating signs and symptoms.

INVESTIGATIONS

CSF PCR or viral culture: positive for the causative virus and negative for West Nile virus. However, a negative PCR does not necessarily exclude viral meningitis.

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

No differentiating signs and symptoms.

INVESTIGATIONS

CSF analysis: high protein, low glucose, CSF Gram stain positive for specific organisms.[62]

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Always suspect in people with a compromised immune system (e.g., AIDS, lymphoma).

INVESTIGATIONS

Cryptococcal polysaccharide antigen: positive in serum or CSF.

Culture: positive for Cryptococcus neoformans in serum or CSF.

CSF microscopy: India ink stain detects the organism.[63]

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

No clear differentiating signs and symptoms.

INVESTIGATIONS

CSF PCR: detection of acid-fast bacilli.

CT/MRI head: can show cerebral tuberculomas or basilar arachnoiditis.[64]

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Typically presents 1 to 8 weeks following acute viral infection.

There is no fever or leukocytosis.

Ascending symmetric weakness.

No bowel or bladder dysfunction.

No concurrent encephalopathy.

INVESTIGATIONS

Diagnosis is usually clinical.[65]

CSF analysis: shows elevated protein, no elevated cell count.

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Residence or travel in endemic area.

Unimmunized status.

Usually clinically and pathologically identical to West Nile poliomyelitis.

INVESTIGATIONS

Virus culture (stool, CSF, or pharynx): positive for poliovirus.

Diagnosis is usually clinical.

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Residence in or travel to an endemic region.

Widespread maculopapular (sometimes morbilliform) rash is common; it is often itchy.

Nonpurulent conjunctivitis or conjunctival hyperemia may be present.

Not associated with neuroinvasive disease but has been associated with Guillain-Barre syndrome (GBS).

INVESTIGATIONS

Reverse transcriptase PCR: positive for Zika virus RNA.

Serology: positive for Zika virus antibodies.

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Residence in or travel to an endemic region.

Biphasic fever and biphasic rash (transient generalized macular rash, followed by a second morbilliform, maculopapular rash).

Bone pain.

INVESTIGATIONS

Serology: positive for dengue virus antibodies.

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Residence in or travel to an endemic region.

Prominent joint symptoms.

Absence of signs of neuroinvasive disease.

INVESTIGATIONS

Reverse transcriptase PCR: positive for Chikungunya virus RNA.

Serology: positive for Chikungunya virus antibodies.

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

There is usually a history of exposure to contaminated water or soil, or contact with infected animals or their depositions.

Neurologic involvement is less common.

Biphasic presentation.

Bilateral conjunctival suffusion is pathognomonic.

Muscle tenderness is localized in calves.

Pulmonary signs and symptoms (e.g., cough, dyspnea).

In severe cases, jaundice, renal failure, and bleeding can occur.

INVESTIGATIONS

PCR: positive for Leptospira RNA.

Serology (microscopic agglutination test): positive for Leptospira antibodies. 

Blood or urine culture: positive for Leptospira.

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Residence in or travel to an endemic region.

Inadequate or absent malaria chemoprophylaxis.

Neurologic involvement is less common.

INVESTIGATIONS

Complete blood count: may show anemia and/or thrombocytopenia.

Giemsa-stained thick and thin blood smears: detection of asexual or sexual forms of the parasites inside erythrocytes.

Rapid diagnostic tests: detection of parasite antigen or enzymes.

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

History of tick bite.

More chronic course and gradual onset.

Erythema chronicum migrans.

Lyme arthritis.

Chronic radicular paresthesias.

INVESTIGATIONS

Positive serum antibody titer for Borrelia burgdorferi: total Lyme titer or positive IgG and IgM.

Western blot (IgM/IgG): to confirm positive titers.[66][67]

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Characteristic rash appears 2 to 6 days after fever onset.

Initially maculopapular eruption that begins on wrists and ankles and spreads to trunk and extremities, involving palms and soles. Later becomes petechial in appearance.[68]

INVESTIGATIONS

Serology: positive for Rickettsia rickettsii.[69]

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Respiratory symptoms and signs, such as cough, chest tightness, crackles, rhonchi, chest tightness.[70]

INVESTIGATIONS

Serology: positive for Legionella species.[70]

Chest x-ray: shows pneumonia.[70]

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Neurologic deficit usually focal.

Symptom onset more gradual.

INVESTIGATIONS

CT/MRI head: shows mass.[71]

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Neurologic deficit usually focal.

Symptom onset more gradual.

INVESTIGATIONS

CT/MRI head: shows abscess.[72]

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Neurologic deficit usually focal.

Progression of signs/symptoms occurs over a few hours, not days or weeks.

INVESTIGATIONS

CT/MRI head: shows infarction and/or hemorrhage.[73]

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Cardiac murmur and signs of congestive heart failure present.

Characteristic but less common features include splinter hemorrhages, Osler nodes, Janeway lesions, and Roth spots.

INVESTIGATIONS

Bacterial blood cultures: positive.

Echocardiogram: shows vegetations.

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Important to consider the current epidemiologic situation. May give history of unwell contacts.

Respiratory symptoms may be prominent.

INVESTIGATIONS

Real-time reverse transcription polymerase chain reaction (RT-PCR): positive for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA. Rapid antigen tests may also be used.

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