Differentials
Alcohol or other sedative or hypnotic drug overdose
SIGNS / SYMPTOMS
History of alternative drug or alcohol intake, bottles of pills, signs of drug use such as needle marks, smell of alcohol.
INVESTIGATIONS
Elevated serum ethanol or levels of other suspected sedative or hypnotic drug. Test according to suspected drug used.
Hypoglycaemia
SIGNS / SYMPTOMS
History of diabetes; patient may be pale and sweaty.
INVESTIGATIONS
Serum glucose <2.8 mmol/L (<50 mg/dL).
Hyponatraemia
SIGNS / SYMPTOMS
Can be a cause of coma but would not normally be confused with benzodiazepine overdose because there is usually a history of preceding illness.
INVESTIGATIONS
Serum sodium <135 mmol/L (<135 mEq/L).
Hyperosmolar coma
SIGNS / SYMPTOMS
Can be a cause of coma but would not normally be confused with benzodiazepine overdose because there is usually a history of preceding illness, such as diabetes.
INVESTIGATIONS
Serum osmolality >320 mmol/kg (>340 mOsm/kg).
Serum glucose >33.3 mmol/L (>600 mg/dL).
Stroke
SIGNS / SYMPTOMS
A history of rapidly developing neurological deficit plus focal neurological signs on examination.
INVESTIGATIONS
Brain CT or MRI shows area of ischaemia or infarction.
Meningitis
SIGNS / SYMPTOMS
The diagnosis of meningitis is normally suggested by a history of fever, headache, and neck stiffness, and is unlikely to be confused with benzodiazepine overdose except in the case of an undifferentiated coma.
INVESTIGATIONS
Fever often present which is not a feature of benzodiazepine overdose.
Abnormal initial blood tests including raised white blood cell count and inflammatory markers.
CSF abnormalities such as elevated protein usually present.
Brain MRI or CT scan may reveal complications such as cerebral oedema.
Encephalitis
SIGNS / SYMPTOMS
Serious, complex, and potentially fatal disorder with non-infectious and infectious causes. Patients usually present with acute onset of a febrile illness and altered mental status; typical features include headache, seizures, and focal neurological signs. Encephalitis is unlikely to be confused with benzodiazepine overdose except in the case of an undifferentiated coma.
INVESTIGATIONS
Raised inflammatory markers.
Findings on CSF analysis and brain MRI often reflect the underlying aetiology.
Post-ictal state
SIGNS / SYMPTOMS
Psycho-motor retardation or other central nervous system depression following seizure may be confused with benzodiazepine overdose, although history of seizure disorder is usually present.
INVESTIGATIONS
EEG may show signs of recent seizure but diagnosis is usually clinical.
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