mc ewan sign in alocohol toxicity
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McEwan sign pupils alcohol coma diagnosis
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Macewen's Sign in Alcohol Toxicity (Alcoholic Coma)
Note on spelling: The sign is named after Sir William Macewen (1848-1924), a surgeon from the University of Glasgow. It is sometimes written "McEwan's sign" but the correct eponym is Macewen's sign.
What is It?
Macewen's sign for alcoholic coma is a pupillary sign used to help distinguish alcoholic coma from other causes of unconsciousness (head injury, opium poisoning, apoplexy, etc.).
Description of the sign:
- In alcoholic coma, the pupils are contracted (miotic) at rest.
- When the patient is subjected to external painful stimulation (e.g., pinching, slapping, shaking), the pupils dilate transiently, then slowly constrict again back to the contracted state.
- This sluggish, reversible dilation in response to painful stimulus - rather than sustained dilation - is the hallmark of alcoholic coma.
In Macewen's own words (1879):
"If on the application of external stimulation, though the personal consciousness refuses to return, the pupil half wakes up and then slowly drops to sleep again... the pupils are more sluggish in their movements, and respond feebly to light and shade."
Clinical Significance
| Feature | Alcoholic Coma | Head Injury / Other |
|---|---|---|
| Resting pupils | Contracted (miotic) | May be dilated or unequal |
| Response to pain | Transient dilation, then slow constriction | Momentary slight enlargement only, or no change |
| Stimulus response quality | Sluggish but present | Absent or immediate constriction |
Macewen studied 50 consecutive cases of suspected alcoholic coma and found this pupillary response present in 49 out of 50 (98%) - making it a highly reliable sign at the time.
Contrast with Macewen's Sign for Hydrocephalus
Macewen described two separate signs:
- Alcoholic coma sign - the pupillary response described above.
- Hydrocephalus/brain abscess sign - percussion of the skull near the junction of the frontal, temporal, and parietal bones produces a "cracked pot" (tympanic) sound, indicating separated sutures from raised intracranial pressure. This is the more widely cited "Macewen's sign" in current clinical teaching.
Summary
Macewen's sign in alcohol toxicity = contracted pupils at rest that transiently dilate with painful external stimulation and then slowly reconstrict - a pattern Macewen described as characteristic of alcoholic coma, helping distinguish it from coma due to structural brain injury or other causes. The original description was published in the Glasgow Medical Journal in January 1879.
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