Test your medicine knowledge with the MKSAP challenge, in partnership with the American College of Physicians.
A 32-year-old man is brought to the emergency department after becoming disoriented, combative, and agitated earlier that day. He is accompanied by a friend, who states that the patient has a history of alcohol and drug abuse, including inhalants.
On physical examination, the patient is uncooperative and slightly disoriented. Temperature is normal, blood pressure is 140/88 mm Hg, and pulse rate is 98/min. The remainder of the examination is normal.
Laboratory studies:
| Fasting glucose | 110 mg/dL (6.1 mmol/L) |
| Sodium | 142 mEq/L (142 mmol/L) |
| Potassium | 4.1 mEq/L (4.1 mmol/L) |
| Chloride | 109 meg/L (109 mmol/L) |
| Bicarbonate | 23 mEq/L (23 mmol/L) |
| Blood urea nitrogen | 18 mg/dL (6.4 mmol/L) |
| Plasma osmolality | 320 mosm/kg H2O (320 mmol/kg H2O) |
| Serum creatinine | 1.1 mg/dL (97.2 µmol/L) |
| Serum ketones | Positive |
| Urinalysis | Trace glucose; 4+ ketones |
Arterial blood gas studies (with the patient breathing ambient air):
| pH | 7.4 |
| Pco2 | 44 mm Hg |
| Po2 | 92 mm Hg |
Which of the following is the most likely cause of this patient’s clinical presentation?
A) Alcoholic ketoacidosis
B) Diabetic ketoacidosis
C) Ethylene glycol
D) Isopropyl alcohol
E) Toluene
MKSAP Answer and Critique
The correct answer is D) Isopropyl alcohol. This item is available to MKSAP 15 subscribers as item 8 in the Nephrology section. More information about MKSAP 15 is available online.
This patient most likely has isopropyl alcohol poisoning. Manifestations of this condition resemble those in ethanol intoxication and include inebriation and a depressed mental status. Isopropyl alcohol ingestion causes acetone production, which results in ketones in the blood and urine. However, because bicarbonate is not consumed during acetone production, metabolic acidosis is absent in this setting. Isopropyl alcohol poisoning is characterized by an increased osmolal gap in the setting of positive serum and urine ketones. The osmolal gap is the difference between the measured and calculated osmolality, with the calculated osmolality obtained using the following formula:
Plasma Osmolality (mosm/kg H2O) = 2 × Serum Sodium (mEq/L) + Blood Urea Nitrogen (mg/dL)/2.8 + Glucose (mg/dL)/18
This patient’s calculated plasma osmolality is 296 mosm/kg H2O (296 mmol/kg H2O) and the calculated osmolal gap is 24 mosm/kg H2O (24 mmol/kg H2O), whereas the normal osmolal gap is approximately 10 mosm/kg H2O (10 mmol/kg H2O). An elevated osmolal gap suggests the presence of an unmeasured osmole and is most commonly caused by ethanol. The osmolal gap is also elevated in the presence of ethylene glycol, methanol, and isopropyl alcohol. However, isopropyl alcohol does not cause an elevated anion gap metabolic acidosis (methanol and ethylene glycol poisoning) and is not associated with retinal abnormalities (methanol poisoning) or kidney failure (ethylene glycol poisoning).
This patient’s confusion and disorientation are consistent with ethylene glycol poisoning, diabetic ketoacidosis, and alcoholic ketoacidosis; however, these conditions would be associated with an anion gap metabolic acidosis. Toluene, an industrial solvent that can be abused as an inhalant, may cause confusion and disorientation in addition to metabolic acidosis, hypokalemia, hypophosphatemia, rhabdomyolysis, and elevated creatine kinase level. The absence of metabolic acidosis and hypokalemia makes toluene poisoning unlikely.
Key Point
- Isopropyl alcohol poisoning is characterized by an increased osmolal gap in the setting of positive serum and urine ketones and does not cause metabolic acidosis.
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