History

The history seldom helps to differentiate amebic meningoencephalitis from other CNS diseases.

Primary amebic meningoencephalitis

Characteristics of PAM are as follows:

PAM commonly affects children and young adults who have previously been healthy
This disease occurs more often during the warmer months of the year and in warmer climates
Patients with PAM typically have a history of swimming, diving, bathing, or playing in warm, generally stagnant, freshwater during the previous 1-9 days
Rarely, patients with PAM may experience disordered smell or taste
Most often, the symptoms of PAM are indistinguishable from those of acute bacterial meningitis.
The acute onset of PAM occurs over a period of hours to 1-2 days

Granulomatous amebic encephalitis

The characteristics of GAE include the following:

It affects individuals of all ages, although those at the extremes of age may be more susceptible
Persons with debility or immunocompromise may be more susceptible to GAE
There is no seasonal variation because the causative pathogens are ubiquitous
Individuals with GAE may have keratoconjunctivitis or a skin ulcer or lesion preceding neurologic symptoms
A subacute or chronic presentation lasting days or weeks

General Presentation

The presentation of primary amebic meningoencephalitis closely mimics that of bacterial meningitis. Patients typically present with fever, headache, nausea, vomiting, photophobia, and stiff neck.^[22]Additional symptoms include confusion, somnolence, seizures, and coma. In all cases reported to date, there has been a history of water entry into the nose.^[23]Symptom onset begins 1-9 days after such an exposure.^[24]

Typical symptoms of GAE include low-grade fever and focal neurologic signs, such as cranial nerve palsies, hemiplegia, ataxia, aphasia, diplopia, and seizures. Patients with GAE may also exhibit behavioral changes, stiff neck, signs of increasing intracranial pressure (ICP), stupor, or coma. Symptom onset ranges from weeks to months after exposure. Interestingly, cases of Balamuthia have been reported with patients’ skin lesions occurring months to years prior to the onset of neurologic manifestations.^[25]

Physical Examination

Physical examination seldom helps to differentiate amebic meningoencephalitis from other CNS diseases.

Primary amebic meningoencephalitis

Patients may uncommonly experience abnormal smell or taste. Typical signs include high fever, photophobia, stiff neck, mental status change, and seizures. PAM may progress rapidly to cerebral herniation secondary to increased intracranial pressure. Rarely, myocarditis may occur, although amoebae are not present in the myocardium on histologic evaluation.

Granulomatous amebic encephalitis

Individuals with GAE may have low-grade fever, photophobia, and/or stiff neck. Focal neurologic findings, such as cranial nerve palsies, hemiplegias, aphasias, ataxias, or diplopia, are observed more commonly. When present, seizures may be focal or generalized. Later in the disease course, GAE patients may demonstrate signs of elevated ICP and cerebral herniation. Keratoconjunctivitis, primarily in people who wear contact lenses, or skin lesions may rarely predate neurologic signs and symptoms.

Differential Diagnoses

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Author

Linda Nguyen, MD Resident Physician, Department of Internal Medicine, Albert Einstein Medical Center

Linda Nguyen, MD is a member of the following medical societies: American College of Physicians, American Medical Association

Disclosure: Nothing to disclose.

Coauthor(s)

Sarah Perloff, DO, FACP Associate Chair for Faculty Affairs, Department of Internal Medicine, Program Director, Infectious Diseases Fellowship, Associate Program Director, Internal Medicine Residency, Einstein Medical Center

Sarah Perloff, DO, FACP is a member of the following medical societies: American College of Physicians, American Osteopathic Association, HIV Medicine Association, Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Chief Editor

Russell W Steele, MD Clinical Professor, Tulane University School of Medicine; Staff Physician, Ochsner Clinic Foundation

Russell W Steele, MD is a member of the following medical societies: American Academy of Pediatrics, American Association of Immunologists, American Pediatric Society, American Society for Microbiology, Infectious Diseases Society of America, Louisiana State Medical Society, Pediatric Infectious Diseases Society, Society for Pediatric Research, Southern Medical Association

Disclosure: Nothing to disclose.

Acknowledgements

Michael D Nissen, MBBS, FRACP, FRCPA Associate Professor in Biomolecular, Biomedical Science & Health, Griffith University; Director of Infectious Diseases and Unit Head of Queensland Paediatric Infectious Laboratory, Sir Albert Sakzewski Viral Research Centre, Royal Children's Hospital

Michael D Nissen, MBBS, FRACP, FRCPA is a member of the following medical societies: American Academy of Pediatrics, American Society for Microbiology, Pediatric Infectious Diseases Society, Royal Australasian College of Physicians, and Royal College of Pathologists of Australasia

Disclosure: Nothing to disclose.

Martin Weisse, MD Program Director, Associate Professor, Department of Pediatrics, West Virginia University

Martin Weisse, MD is a member of the following medical societies: Ambulatory Pediatric Association, American Academy of Pediatrics, and Pediatric Infectious Diseases Society

Disclosure: Nothing to disclose.

Mary L Windle, PharmD Adjunct Associate Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Nothing to disclose.