Practice Essentials

Hyperammonemia is a metabolic condition characterized by elevated levels of ammonia in the blood. Increased entry of ammonia to the brain is a primary cause of neurologic disorders, such as congenital deficiencies of urea cycle enzymes, hepatic encephalopathies, Reye syndrome, several other metabolic disorders, and some toxic encephalopathies.^[1]

Signs and symptoms

Signs and symptoms of early-onset hyperammonemia (neonates) may include the following:

Lethargy
Irritability
Poor feeding
Vomiting
Hyperventilation, grunting respiration
Seizures

Signs and symptoms of late-onset hyperammonemia (later in life) may include the following:

Intermittent ataxia
Intellectual impairment
Failure to thrive
Gait abnormality
Behavior disturbances
Epilepsy
Recurrent Reye syndrome
Protein avoidance
Rarely, episodic headaches and cyclic vomiting

See Clinical Presentation for more detail.

Diagnosis

No specific physical findings are associated with hyperammonemia. Affected infants usually present with the following:

Dehydration
Lethargy
Tachypnea
Hypotonia
Bulging fontanelle

Examination occasionally reveals a peculiar finding, such as odor of "sweaty feet" in isovaleric acidemia or abnormally fragile hair in argininosuccinic aciduria. Infants with argininosuccinic lyase deficiency may present with hepatomegaly.

Lab tests

Perform the following tests in patients with suspected hyperammonemia:

Arterial blood gas analysis
Serum amino acid levels
Urinary orotic acid levels
Urinary ketone tests
Plasma and urinary organic acid levels

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Media Gallery

CT scan of cerebral edema caused by hyperammonemia. Republished with permission of American Society of Neuroradiology from U-King-Im JM, Yu E, Bartlett E, Soobrah R, Kucharczyk W. Acute hyperammonemic encephalopathy in adults: imaging findings. AJNR Am J Neuroradiol. 2011 Feb;32(2):413-8; permission conveyed through Copyright Clearance Center, Inc.

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#author-disclosures{display:block}#author-disclosures.modal-layer{position:relative}#author-disclosures .modal-content{max-height:none}#author-disclosures .close-modal{display:none}

Author

Jasvinder Chawla, MD, MBA Chief of Neurology, Hines Veterans Affairs Hospital; Professor of Neurology, Loyola University Medical Center

Jasvinder Chawla, MD, MBA is a member of the following medical societies: American Academy of Neurology, American Association of Neuromuscular and Electrodiagnostic Medicine, American Clinical Neurophysiology Society, American Medical Association

Disclosure: Nothing to disclose.

Coauthor(s)

Gurjot Singh MD Candidate, Aureus University School of Medicine

Gurjot Singh is a member of the following medical societies: American Academy of Family Physicians

Disclosure: Nothing to disclose.

Specialty Editor Board

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Nicholas Lorenzo, MD, CPE, MHCM, FAAPL Co-Founder and Former Chief Publishing Officer, eMedicine and eMedicine Health, Founding Editor-in-Chief, eMedicine Neurology; Founder and Former Chairman and CEO, Pearlsreview; Founder and CEO/CMO, PHLT Consultants; Former Chief Medical Officer, MeMD Inc

Nicholas Lorenzo, MD, CPE, MHCM, FAAPL is a member of the following medical societies: Alpha Omega Alpha, American Academy of Neurology, American Association for Physician Leadership

Disclosure: Nothing to disclose.

Chief Editor

Stephen L Nelson, Jr, MD, PhD, FAACPDM, FAAN, FAAP, FANA Professor of Pediatrics, Neurology, Neurosurgery, and Psychiatry, Medical Director, Tulane Center for Autism and Related Disorders, Tulane University School of Medicine; Pediatric Neurologist and Epileptologist, Ochsner Hospital for Children; Professor of Neurology, Louisiana State University School of Medicine

Stephen L Nelson, Jr, MD, PhD, FAACPDM, FAAN, FAAP, FANA is a member of the following medical societies: American Academy for Cerebral Palsy and Developmental Medicine, American Academy of Neurology, American Academy of Pediatrics, American Epilepsy Society, American Medical Association, American Neurological Association, The Society of Federal Health Professionals (AMSUS), Child Neurology Society, Southern Pediatric Neurology Society

Disclosure: Nothing to disclose.

Additional Contributors

J Stephen Huff, MD, FACEP Professor of Emergency Medicine and Neurology, Department of Emergency Medicine, University of Virginia School of Medicine

J Stephen Huff, MD, FACEP is a member of the following medical societies: American Academy of Neurology, American College of Emergency Physicians, Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Elena Crisan, MD Neurology Staff, Department of Neurology, Edwards Hines Veterans Affairs Hospital; Assistant Professor of Neurology, Loyola University Medical Center

Disclosure: Nothing to disclose.

Acknowledgements

The authors and editors of Medscape Reference gratefully acknowledge the contributions of previous author Kazi Imran Majeed, MD to the development and writing of this article.

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