If a patient suffers from neurological symptoms, lots of differential diagnoses have to be considered. The following article is organized according to the different pathogens: bacteria, viruses, protozoa, and fungi. Learn and repeat everything from the approach at acute bacterial meningitis to virally triggered CNS infections with HSV, FSME, VZV, and CMV, and to opportunistic infections in immunodeficients. This way, no neurological question in the second state examination concerning infectious diseases of the CNS remains unclear!

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Gold standard cerebrospinal fluid examination

Spinal anaesthesia

Image: “Spinalanesthesia” by MrArifnajafov. License: CC BY 3.0

In our part of the world, you will mostly encounter bacterial and viral causes. CNS infections with parasitic causes are very rare due to high hygiene standards. Another reason to differentiate the pathogen classes is the therapeutic approach.

Only at bacterial CNS infections, treatment with antibiotics is reasonable!

Concerning diagnostics, lumbar puncture with following cerebrospinal fluid (CSF) examination is the gold standard. The following aspects are examined in the fluid:

  • Cell count and cell differentiation
  • Glucose and protein
  • Microbiological pathogen detection: direct pathogen detection with microscopy, PCR, antigen detection and cultivation, and indirect pathogen detection with intrathecal production of antibodies against pathogens

Overview of typical cerebrospinal fluid findings at CNS infections

Cells Protein Glucose Lactate
Bacterial Meningitis Often > 1,000 cells/µl, dominantly granulocytic ↑  (100 – 200 mg/dl) ↓ CSF/serum glucose ratio < 0.3
Tubercular Meningitis 50 – 400 cells/µl, first granulocytes, later lymphocytes and monocytes ↑↑  (100 – 500 mg/dl) ↓ CSF/serum glucose ratio  < 0.5 ↑↑
Viral Meningitis < 1,000 cells/µl, dominantly lymphocytic ↑  (e.g.: 50 – 150 mg/dl) Normal

CSF/serum glucose ratio

The CSF/serum glucose ratio gives the relation of glucose in the cerebrospinal fluid compared to glucose in the serum.

Table: A. Bender et al.: mediscript Kurzlehrbuch Neurologie. Elsevier Verlag 2013. S. 191, Tab. 7.2

Bacterial infections of the central nervous system

Acute bacterial meningitis

Epidemiology of bacterial meningitis

At acute bacterial meningitis, the meninges and the subarachnoid cavity are infected. Incidence in Europe: 2-6/100,000 affected people. The disease is significantly more frequent in the meningismus belt in the sub-Saharan regions of Africa. At bacterial meningitis, different pathogens are typical for respective age groups with empiric antibiotic therapy.

  • Newborns: enterobacteria, streptococci, Listeria monocytogenes ⇒ Therapy: cefuroxime and ampicillin
  • Children: Streptococcus pneumoniae, Neisseria meningitidis ⇒ Therapy: Ceftriaxone
  • Adults: Streptococcus pneumoniae, Neisseria meningitidis, Listeria monocytogenes (in > 50-year-olds) ⇒ Therapy: ceftriaxone and ampicillin
Meningitis Epidemics World Map

Image: Demography of meningococcal meningitis. License: Public Domain

Clinic of bacterial meningitis

Cardinal symptoms: Headache, neck stiffness, fever, decrease in vigilance (the symptoms do not always occur in this combination!)

Also, patients often show the following symptoms: nausea, vomiting, vertigo, and photophobia. One third of patients display focal neurological deficits like palsies, sensitivity impairments, and speech disorders occur; one tenth also shows cranial nerve damages. Kernig’s sign and Brudzinski’s sign can be positive (see the article on neurological examination). In infections with Neisseria, skin bleedings in the context of Waterhouse-Friderichsen syndrome are possible.

Diagnostics of Bacterial Meningitis

CSF examination: The examination of the CSF is the diagnostic basis. The pathogens in the CSF can be detected using the Gram stain, CSF cultures, antigen quick tests, PCR, and blood cultures. Cases of acute bacterial meningitis produce the following picture (before treatment):

  • > 1,000 cells/µl, granulocytes dominate
  • Protein and albumin ↑
  • Glucose ↓, CSF/serum glucose ratio < 0.3
  • Lactate ↑
CAVE: If there is clinical evidence to suggest increased cranial pressure (decrease in vigilance, focal neurological deficits, epileptic seizures), a CCT before lumbar puncture is absolutely necessary. (see scheme below)

Blood: The differential blood count mostly shows leukocytosis with left shift, CRP ↑, and procalcitonin ↑.

Imaging: The CT of the skull checks for:

  • Signs of increased cranial pressure at diffuse brain edema or hydrocephalus
  • Changes in density due to accumulations of purulence in the ventricles
  • Abscesses
  • Inflammatory foci in the paranasal sinus and the mastoid

Therapy of bacterial meningitis

Important: Antibiotic therapy should start as soon as possible! The antibiotic therapy should – if possible – be started within 60 minutes after hospitalization.

Since waiting leads to a worse prognosis, the antibiotic therapy is initiated before final pathogen detection according to the typical pathogens of the respective age group (see above under epidemiology). If the pathogen detection has been made, the antibiotic therapy has to be adjusted. Of course, blood cultures are taken BEFORE medicamentous therapy!

For adults with pneumococci meningitis, an adjuvant therapy with dexamethasone is currently (2015) suggested. Studies show decreased occurrence of consequential damages like hearing damages and lethality.

Learning tip: The IMPP and oral exams often ask for the ‘listeria gap’: For adults, ampicillin has to be given in addition to ceftriaxone since ceftriaxone has no effect on listeria.

Prognosis of bacterial meningitis

Lethality of bacterial meningitis is high. 20 % of all patients die of infections caused by the pathogens pneumococci and listeria. With S. aureus as the actuator of acute bacterial meningitis, lethality even is 20-40 %. Possible consequential damages are – among others – hearing damages, neuropsychological deficits, hemiparesis, epileptic seizures, and cranial nerve palsies.

Features of meningococcic meningitis

N. meningitidis is transmitted via droplet infection. In case of suspicion, the affected persons have to be isolated until 24 hours after the start of antibiotic therapy. Contact persons should be treated with a combined chemoprophylaxis consisting of rifampicin, ciprofloxacin/or ceftriaxone in the sense of post-exposition prophylaxis.

Meningococcic meningitis is subject to mandatory reporting at the public health department.

Tubercular meningitis

Epidemiology of tubercular meningitis

The pathogens responsible for tubercular meningitis are mycobacteria out of the Mycobacterium tuberculosis complex. The subacutely or chronically proceeding disease often presents itself as basal meningitis (infectious reaction concentrates on basal cerebral areas, especially the brain stem).

Number-facts for active tuberculosis:

  • Worldwide 10 million people
  • Germany: 4,500 cases

Clinic of tubercular meningitis

Clinical symptoms of tubercular meningitis are primarily fever, meningismus, headaches, nausea, and vomiting. In 50 % of the patients, cranial nerve palsies, disorders in vigilance, and confusion syndromes occur. If encephalitis or tuberculomas form, epileptic seizures are also possible.

Diagnostic of tubercular meningitis

CSF examination: pleocytosis with 50-400 cells/µl, protein ↑↑, glucose ↓ (CSF/serum glucose ratio < 0.5), lactate ↑

Interferon-γ release assays: Blood lymphocytes are stimulated with tuberculosis-antigens. In the case of undergone or current infection, the gained cells produce interferon-γ.

Microbiology: At pathogen detection in CSF with Ziehl-Neelsen stain, Auramin stain, PCR, and cultures, acid-fast rods can be found in tuberculosis. Do not wait until the final pathogen detection (like at acute bacterial meningitis) before beginning therapy!

Imaging: Cerebral changes at tuberculosis are often visible in MRI or CCT.

  • Hydrocephalus
  • Basal contrast agent accumulation
  • Masses at CNS tuberculomas
  • Ischemic infarction in case of associated vasculitis

Therapy of tubercular meningitis

Initially, a fourfold-combination is used as standard therapy. Mostly, it consists of isoniazid, rifampicin, pyrazinamide, and ethambutol.

Learning tip: The ‘IMPP classic’: The initial fourfold-combination of tuberculosis therapy and the side effects of the individual components.
Medication Duration of Application Side Effects
Isoniazid 2 months initially, further 10 months (stabilization phase) Hepatotoxicity, polyneuropathy (prophylaxis pyridoxine)
Rifampicin 2 months initially, further 10 months (stabilization phase) Hepatotoxicity
Pyrazinamide 2 months initially Hepatotoxicity
Ethambutol 2 months initially Impaired vision (ophthalmologic controls are regularly necessary)
Streptomycin 2 months initially Ototoxicity

Prognosis of tubercular meningitis 

If no antibiotic therapy is performed, tubercular meningitis mostly ends lethally. If sufficient treatment is performed, lethality is reduced to roughly 20 %. Circa 30 % of the affected people suffer from consequential damages like hydrocephalus, organic brain syndrome, cranial nerve palsies, ataxia, and epileptic seizures.

Brain abscess

Etiology of brain abscesses

Brain abscess

Image: “Hirnabszess in der MRT” by Hellerhoff. License: CC BY-SA 3.0

A brain abscess is a bacterial abscessing infection of the brain.

Brain abscesses can form in different ways: via transmission of meningeal foci, hematogenic, and iatrogenic in the course of surgical interventions. The pathogens responsible for this are mostly streptococci, anaerobics, Gram-negative enterobacteria, pseudomonads, and S. aureus. At immunodeficiency, fungi and parasites can also be the actuators of abscesses.

Clinic of the brain abscess

At brain abscesses, there is a broad variety of symptoms which can develop over days or weeks. They include:

  • Headache
  • Fever
  • Nausea and vomiting
  • Epileptic seizures
  • Neurological examination: vigilance impairments, meningismus

Diagnostic of the brain abscess

Laboratory, microbiology, and imaging procedures: In laboratory parameters, CRP is mostly increased; CSF examination is not necessary since the findings are too unspecific. More important is the examination of abscess material via bacterial cultivation, PCR, and the test for fungi and mycobacteria.

Therapy of the brain abscess

The 3 Pillars of Brain Abscess Therapy
Surgical removal of purulenceCAT/MRI-controlled stereotactic aspiration. Goal: reduction of the mass, gain of material for microbiological diagnostics

If necessary, excision at foreign bodies and division of abscesses

Systemic antibiosisBefore pathogen detection empiric three-fold therapy:

1. Cephalosporin of 3rd generation (e.g. ceftriaxone)

2. Antibiotic against anaerobics (e.g. metronidazole)

3. Antibiotic against staphylococci (e.g. vancomycin)

⇒ Adjustment according to the antibiogram

Elimination of the Infectious FocusThorough search for the focus (is the focus located distally?) with surgical elimination if needed

Prognosis of the brain abscess

In case of timely and appropriate therapy, lethality is < 10 %.


Epidemiology of neuroborreliosis

Neuroborreliosis, triggered by the bacterium Borrelia burgdorferi, which is transmitted by ticks, is one of the most frequent CNS diseases in Germany: 100-50 / 100,000 inhabitants suffer from this disease. The regional dissemination of the infected ticks is very different and should be taken into account for diagnosis.

Clinic of neuroborreliosis

The symptoms of neuroborreliosis typically proceed in three stages:

  • Stage I: Formation of erythema migrans: circularly limited skin reddening, which mostly develops ca. 2 weeks after the tick bite. Only half of the patients who reach stage II had erythema migrans.
Erythema motilans

Image: “Erythema motilans at lower leg of a man” by Hellerhoff. License: CC BY 2.0

  • Stage II: Meningoradiculitis: searing, radicular pain (Bannwarth syndrome), partially radicular palsies, palsy of the facial nerve. Joint involvement, myocarditis, pericarditis, and lymphadenosis cutis benigna are also possible.
  • Stage III: Detection of antibodies against B. burgdorferi in the enzyme-immune-essay. The detection of antibodies has to occur in both the serum and the CSF. The antibodies are not suitable for therapy assessment! The antibodies can circulate in the CSF over the course of months to years after successful antibiosis.

Therapy of neuroborreliosis

Erythema migrans is treated with an oral 14-day antibiosis: amoxicillin, cefuroxime, doxycycline, or penicillin. If neuroborreliosis has reached stage II or III, oral therapy should be performed with doxycycline over 14 days. The alternative is intravenous treatment with ceftriaxone, cefotaxime, or pencillin.

Prophylaxis of neuroborreliosis

If a tick is removed within the first 12 hours after the bite, the risk of borrelia infection is decreased. There is no vaccination against borrelia.

Viral infections of the central nervous system

The most common viruses causing CNS infection are herpes-simplex-virus (HSV), varizella-zoster-virus (VZV), HIV, Ebstein-Barr-virus (EBV), and enteroviruses.


Epidemiology of herpes-simplex-virus-encephalitis

The herpes-simplex-virus encephalitis is rare, but it has a fulminant course. Incidence amounts to 1/250,000 inhabitants.

Clinic of herpes-simplex-virus-encephalitis

Besides possible aphasia, ataxia, hemiparesis, cranial nerve palsies, and visual field deficits, especially these cardinal symptoms of herpes-simplex-virus-encephalitis occur:

  • High fever
  • Headache
  • Personality changes
  • Epileptic seizures in 60 %
  • NO meningismus

Diagnostic of herpes-simplex-virus-encephalitis

CSF: CSF findings mostly show a typical relation: lymphomonocytic pleocytosis, elevated protein and albumin, and non-decreased glucose (see the table concerning typical CSF findings in bacteria and viruses above).

Microbiology: With PCR, HSV-DNA is detected in the CSF.

Imaging procedures and EEG: Mostly, the temporal lobe is affected most. Necrosis and hemorrhages are typical signs. The EEG often shows temporal slowdowns.

Hsv encephalitis

Image: “Herpes-simplex-Enzephalitis” by Dr Laughlin Dawes. License: CC BY 3.0

Therapy and prognosis of herpes-simplex-virus-encephalitis

The medicamentous therapy consists of intravenous injection of aciclovir over 14 days. Despite timely introduced therapy, 20 % of all diseased people die. Most survivors suffer from consequential diseases.

Viral meningitis

Epidemiology of viral meningitis

Incidence of viral meningitis is 6-10/100,000 inhabitants. In Germany, mostly enteroviruses are the actuating pathogens. HHV6, VZV, measles viruses, mumps viruses, and EBV also should be taken into account.

Clinic of viral meningitis

Viral meningitis causes the typical picture of a meningitic disease: fever,neck stiffness, and headache. Often, patients also display flu symptoms.

Diagnostic and therapy of viral meningitis

The CSF findings show the typical picture for viruses with elevated protein and non-decreased glucose levels. Microbiologically, PCR and indirect serological pathogen detections are used.

If viral meningitis is caused by VZV or HSV, treatment with aciclovir is reasonable. If, however, enteroviruses are the cause, only symptomatic treatment occurs.

Herpes zoster: the shingles

Herpes zoster

Image: “Herpes zoster” by Fisle. License: CC BY 3.0

Etiology of herpes zoster

If an earlier varizella-zoster-infection (chickenpox) reactivates, herpes zoster develops. This is often an expression of immunodeficiency. However, herpes zoster may also occur in immunocompetent people.

Clinic of herpes zoster

Typically, after a painful phase, skin reddening with blister formation in the dermatome of a nerve root sets in. Especially severe are disease courses in facial dermatomes: zoster oticus and zoster opthlamicus. A frequent complication is poster-zoster-neuralgia with pain and allodynia.

Diagnostic and therapy of herpes zoster

Mostly, the diagnosis of herpes zoster is made on the basis of the dermatological picture. Very occasionally, pathogen detection with blister secretion and biopsy material is used.

The virostatics aciclovir, brivudin, famciclovir, or aciclorvir can be used orally for treatment of uncomplicated herpes zoster. In severe cases, intravenous therapy is indicated.

Early summer meningoencephalitis (ESME)

Etiology of ESME

Early summer meningoencephalitis is actuated by the flavivirus, which is – like borrelia – transmitted by ticks. Also, there is a different regional dissemination in Germany.

Clinic of ESME

Early summer meningoencephalitis proceeds in two phases:

  • Phase I: 8-10 days after the infection, the patient has flu-like symptoms
  • Phase II: 1 week fever-free interval, then vigilance disorders, confusion syndrome, stand and gait ataxia, intention tremor, extrapyramidal symptoms

Diagnostic, therapy, and prevention of ESME

Typical for early summer meningoencephalitis is a CSF syndrome with lymphocytic pleocytosis, blood-liquor barrier disorders, positive detection of ESME-IgM and IgG-antibodies, and intrathecal ESME-specific antibody production 2 weeks after disease onset.

At ESME, therapy can only occur symptomatically. People living and working in risk areas should vaccinate.

Progressive multifocal leukoencephalopathy (PML)

Etiology of PML

The pathogen of PML is the JC-virus, which leads to demyelination of white matter at infections. Mostly, the disease occurs at immunodeficiency, like T-cell-defects. While it almost exclusively affected HIV-patients in the past, PML now also frequently affects people, who are medically immunosuppressed due to multiple sclerosis.

Clinic of PML

Depending on the localization of the demyelination focus, symptoms like behavioral problems, cognitive deficits, palsies, visual impairments, vigilance disorders, and speech disorders can show.

Diagnostic and therapy of PML

JC-viruses can be detected in CSF via PCR. In the MRI, typical signs of PML are confluent demyelination foci without contrast agent accumulation.

Therapeutically, only an improvement of immunocompetence is possible. Antiviral therapy does not (yet) exist. Affected patients with PML do not have a good prognosis: Often, the patients die within two years.

Cytomegalovirus (CMV)-infection

CMV-infection occurs in the course of AIDS-disease at very severe immunosuppression. In imaging procedures, the infection shows micronodular changes in the brain and/or hydrocephalus. With PCR, the viruses can be detected in CSF. Concerning therapy, ganciclovir is used.

Protozoa- and fungal infections of the central nervous system: facts-overview

The following overview allows a quick access to facts concerning the most important CNS-diseases caused by protozoa and fungi.

Cerebral Toxoplasmosis Cryptococci-Meningoencephalitis CNS-Aspergillosis Cysticercosis
Etiology AIDS-defining disease, parasite: Toxoplasma gondii AIDS-defining disease, fungal infection, especially with Cryptococcus neoformans Mold fungus infection with Aspergillus fumigatus, does not occur until severe immunosuppression Consumption of contaminated meat, infection with eggs of the pork tapeworm Taenia solium causes cysts in the brain
Clinic Personality change, palsy sensations, sensibility disorders, visual impairments (toxoplasmosis-choriorenitis), speech disorders, epileptic seizures, headaches Meningoencephalitis with headaches, fever, and vigilance disorders, focal neurological deficits like palsies, sensibility disorders, and visual impairments Depending on the location of manifestation, frequent affliction of the lung and the paranasal sinuses: dyspnea, hemoptysis, sinusitis, lung infiltration, bronchial asthma Depending on the location of the cysts: often epileptic seizures
Diagnostic Imaging: multiple circular contrast agent accumulating lesions. Laboratory: antibodies against toxoplasmosis Imaging: inconspicuous MRI, germ detection in tusche specimen, with PCR, cultures, positive antigen detection in blood and CSF Imaging: Abscess in the brain, ischemic and hemorrhagic infarctions. Laboratory: aspergillus-antigen in blood and CSF, cultures, PCR, histological detection in biopsy material Imaging: Detection of cerebral cysts, detection of the head of the worm (scolex). Laboratory: intermittent eosinophilia is frequent
Therapy Sulfadiazine or clindamycin and pyrimethamine for at least 4 weeks, then reduced dose for 6 months Amphothericin B and fluconazole for 6 weeks, then continuation therapy with fluconazole Voriconazole Prognosis: Rate of lethality is rather bad at invasive CNS-aspergillosis. Praziquantel (stationary due to edema formation), surgical, if cysts are operable

Opportunistic diseases with HIV

Immunosuppression in AIDS-patients leads to several disease, which manifest in the CNS. Mostly, the diagnosis AIDS is made on the basis of so-called AIDS-defining diseases. They occur if certain levels of CD4-cells are undercut.

  • CNS-toxoplasmosis (at < 100/µl)
  • Primary CNS-lymphomas (no limit)
  • Cerebral Cryptococci-infections (at < 100/µl)
  • CNS-tuberculosis (no limit)
  • CMV-encephalitis (at < 50/µl)
  • PML (at < 250/µl)

Popular exam questions concerning infectious diseases of the CNS

The answers can be found below the references.

1. Which medicament is not used at neurotuberculosis?

  1. Isoniazid
  2. Rifampicin
  3. Amphotericin
  4. Pyrazinamide
  5. Ethambutol

2. The CSF finding presents like this: > 1,000 cells/µl with dominantly granulocytes, protein, and albumin , glucose , CSF/serum glucose ratio < 0.3, lactate. For which disease are those parameters typical?

  1. Cryptococci-meningoencephalitis
  2. Bacterial meningitis
  3. CMV-meningitis
  4. Neuroborreliosis
  5. Brain abscess

3. Which assignment of typical bacteria, age, and treatment is not correct concerning bacterial meningitis?

  1. Newborns: streptococci group B, cefuroxime and ampicillin
  2. Children: Streptococcus pneumoniae, ceftriaxone
  3. Adults: Neisseria meningitidis, ceftriaxone and ampicillin
  4. Children: Listeria monocytogenes, ceftriaxone
  5. Newborns: enterobacteria, cefuroxime and ampicillin



Bender et al.: mediscript Kurzlehrbuch Neurologie. Elsevier Verlag 2013

Robert-Koch-Institut RKI-Ratgeber für Ärzte zum Infektionsschutz via rki.de

Correct answers: 1C, 2B, 3D

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