Spinal tap (lumbar puncture)
This procedure helps to rule out other diseases with similar signs and symptoms, such as infection of the lining and fluid that surround your brain and spinal cord (meningitis) or inflammation or infection of the brain (encephalitis). Local anesthesia is used to numb the puncture site in the lower back. A needle is then inserted through the lower back into the space around the spinal cord to collect a small sample of cerebrospinal fluid (CSF). The CSF can be analyzed for protein, sugar, and red and white blood cells. The sample is also routinely cultured to identify bacterial and viral infections.
Generally, this procedure is done by inserting a thin needle through the skin on the upper right side of the abdomen and into the liver in order to draw a tissue sample from the liver for laboratory analysis. This analysis is then used to rule out other possible diseases that may be affecting the liver.
Detecting rare metabolic disorders
Doctors may want to evaluate the possibility that the child has one of the rare, inherited metabolic disorders that can mimic the signs and symptoms of Reye’s syndrome. The list of these metabolic disorders is long, and most of them have long unfamiliar terms, such as medium-chain acyl-CoA dehydrogenase (MCAD) deficiency. Most, if not all, of these conditions are inherited and may occur with varying degrees of severity in other family members.
The key to diagnosing or excluding these unusual conditions is obtaining blood and urine samples during the acute phase of the illness and having them analyzed in a qualified biochemical genetics laboratory. Many of these metabolic conditions are termed mitochondrial diseases because the problems arise from the part of body cells called the mitochondria.
If a child dies of a Reye’s-like illness, it may be important to obtain blood and urine to check for these metabolic conditions. Collecting samples of liver and brain tissue shortly after death could be the key to diagnosing a condition that might affect other family members. It may even be possible to analyze tissue from an autopsy done many years ago to clarify whether a death was due to a metabolic cause.
- On liver function testing, ammonia levels are as much as 1.5 times normal (up to 1200 mcg/dL) 24-48 hours after the onset of mental status changes is the most frequent laboratory abnormality. Ammonia levels may return to the reference range in stages 4 and 5. Levels of transaminases, ALT, and AST increase to 3 times normal but may return to the reference ranges by stages 4 or 5.
- Bilirubin levels are >2 mg/dL (usually <3 mg/dL) in 10-15% of patients. If direct bilirubin is more than 15% of total. If the total is >3 mg/dL, consider other diagnoses.
- The prothrombin time (PT) and activated partial thromboplastin time (aPTT) are prolonged >1.5-fold in >50% of patients.
- Lipase and amylase levels are elevated.
- Serum bicarbonate levels are decreased secondary to vomiting.
- BUN and creatinine levels are elevated.
- Expect hypoglycemia, particularly in children younger than 1 year. A serum glucose test is indicated for all children with altered mental status.
- Lactic dehydrogenase (LDH) levels may be high or low.
- Obtain an anion gap test for metabolic acidosis.
- Urine specific gravity is increased; 80% of patients have ketonuria.
- These laboratory abnormalities may be transient.
- Head CT scanning may reveal cerebral edema, but the results are usually normal.
- Levels of free fatty acids and amino acids (eg, glutamine, alanine, lysine) may be elevated.
- Factor assays show decreased factors II, VII, IX, and X and in fibrinogen due to the disruption of synthetic activities in the liver.
- An electroencephalogram (EEG) may reveal slow-wave activity in the early stages and flattened waves in advanced stages.
- On CSF testing, opening pressure may or may not be increased. WBCs (usually lymphocytes) may be 9 X 109/L (<9/mm3).
- An extensive metabolic workup to exclude IEM must be performed and should include evaluation for defects of fatty-acid oxidation, amino and organic acidurias, urea-cycle defects, and disorders of carbohydrate metabolism.
- Percutaneous liver biopsy may be indicated to exclude IEM or toxic liver disease.
- Correction of any coagulopathy before the procedure is important.