This page reveals the answer
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Five progressive clues
These are the case findings in their original reveal order, moving from the broader presentation to the most discriminating evidence.
Clue 1
A 19-year-old man is brought to the emergency department by his roommate, who found him confused and restless a few hours after a breakup. The roommate says he swallowed most of a bottle of an over-the-counter antihistamine sleep aid, and now he keeps mumbling and reaching for objects that are not there.
Clue 2
The roommate estimates he took about twenty-five 25 mg tablets roughly two hours before arrival; there is no alcohol, no other medication, and no history of recreational drug use. Since then he has grown steadily more agitated and incoherent, cannot sit still, and between mumbled phrases complains that he feels hot, that his mouth is parched, and that he cannot urinate.
Clue 3
On examination his skin is flushed, warm, and completely dry, with no sweat anywhere despite his obvious fever; his oral mucosa is dry and tacky. His pupils are dilated to about 7 mm bilaterally and only sluggishly reactive, his bowel sounds are markedly diminished, and his lower abdomen is distended and tender over a palpable bladder.
Clue 4
Vitals: temperature 38.9 C, heart rate 128 and regular, blood pressure 148/88, respirations 18, oxygen saturation 98 percent. A bladder scan shows 600 mL of retained urine. The 12-lead ECG shows sinus tachycardia with a normal QRS duration of 92 ms, serum CK is normal, and there is no clonus or muscular rigidity on repeat neurologic exam.
Diagnosis
Anticholinergic Toxicity
Why the diagnosis fits
The full toxidrome here — hyperthermia with warm, flushed, bone-DRY skin, mydriasis, urinary retention, absent bowel sounds, and an agitated hyperactive delirium with visual hallucinations — is the classic peripheral-plus-central muscarinic blockade picture, and a large diphenhydramine ingestion is a textbook cause. The single key discriminator from a sympathomimetic overdose (which shares the fever, tachycardia, mydriasis, and agitation) is the skin: sympathomimetic toxicity produces profuse DIAPHORESIS, whereas muscarinic blockade produces dry skin with urinary retention and ileus. A normal QRS argues against tricyclic sodium-channel toxicity, and absent clonus/rigidity with a normal CK excludes serotonin syndrome and neuroleptic malignant syndrome; prompt reversal of the delirium and tachycardia by an acetylcholinesterase inhibitor confirms the mechanism.
Educational reference
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Open the clinical referenceFor education and entertainment only. This fictional case is not medical advice and does not replace supervised clinical training, diagnosis, or treatment.