Differential Diagnosis
- Single most likely diagnosis
- Urea cycle disorder: The patient's extremely high ammonia level (1266 µg/dL) is a strong indicator of a urea cycle disorder. These disorders lead to an accumulation of ammonia, which is toxic to the brain, causing symptoms such as lethargy, vomiting, and seizures.
- Other Likely diagnoses
- Fatty acid oxidation disorder: Although less likely than a urea cycle disorder given the ammonia level, fatty acid oxidation disorders can present with similar symptoms, including lethargy, vomiting, and seizures, especially during periods of fasting or when the body is under stress.
- Mitochondrial disorder: Mitochondrial disorders can affect energy production and lead to a variety of symptoms, including those seen in this patient. However, the specific pattern of laboratory abnormalities, particularly the very high ammonia level, makes this less likely.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Adrenal deficiency: Although the clinical presentation and lab values do not strongly suggest adrenal deficiency, it is a condition that could lead to severe illness and death if not promptly treated. The patient's low blood pressure and poor perfusion could be indicative of adrenal crisis, but the primary issue appears to be related to ammonia toxicity.
- Infection or sepsis: The patient's presentation with lethargy, vomiting, and seizures could also be indicative of an infectious process, particularly given the deep and rapid respirations and low oxygen saturation. However, the laboratory findings, especially the ammonia level, point more towards a metabolic disorder.
- Rare diagnoses
- Lysosomal storage disease: These diseases are a group of rare inherited disorders caused by defects in lysosomal function, leading to an accumulation of toxic substances within cells. While they can present with a wide range of symptoms, the acute presentation with hyperammonemia is less typical for lysosomal storage diseases.
- Organic acidemias: These are disorders of amino acid metabolism that can lead to the accumulation of toxic compounds, including ammonia. However, the specific pattern of abnormalities, particularly the very high ammonia level without mention of specific organic acid elevations, makes urea cycle disorder more likely.