Differential Diagnosis for a 29-year-old Male with Acute Altered Mental Status

Single Most Likely Diagnosis

• Serotonin Syndrome: Given the patient's history of taking antidepressants like amitriptyline and mirtazapine, and presenting with symptoms such as altered mental status, restlessness, tachycardia, and hypertension, serotonin syndrome is a highly plausible diagnosis. The presence of rhabdomyolysis further supports this, as it is a known complication of serotonin syndrome.

Other Likely Diagnoses

• Neuroleptic Malignant Syndrome (NMS): Although less likely than serotonin syndrome due to the specific medications mentioned, NMS could still be considered given the overlap in symptoms such as altered mental status, tachycardia, hypertension, and rhabdomyolysis.
• Substance-Induced Psychosis: Despite the patient's denial of drug abuse, the possibility of substance-induced psychosis cannot be entirely ruled out, especially given the acute presentation and behavioral disturbances.
• Vitamin Deficiency-Related Encephalopathy: Certain vitamin deficiencies, such as Wernicke's encephalopathy (thiamine deficiency), can present with altered mental status and could be considered, especially if there's a suspicion of malnutrition or poor dietary habits.

Do Not Miss Diagnoses

• Intracranial Hemorrhage or Stroke: These conditions can present with acute altered mental status and require immediate intervention to prevent further brain damage or death.
• Meningitis or Encephalitis: Infections of the brain or meninges can cause altered mental status, fever, and other systemic symptoms, and are medical emergencies.
• Severe Hyponatremia or Hypernatremia: Electrolyte imbalances can lead to altered mental status and seizures, and correcting these imbalances is crucial to prevent further complications.

Rare Diagnoses

• Wilson's Disease: A genetic disorder that leads to copper accumulation in the brain and liver, which can cause psychiatric symptoms, tremors, and liver dysfunction.
• Porphyrias: A group of disorders that can lead to acute neurological symptoms, including altered mental status, due to the accumulation of porphyrin precursors.
• Hashimoto's Encephalopathy: A rare condition associated with Hashimoto's thyroiditis, characterized by altered mental status, seizures, and stroke-like symptoms, which improves with corticosteroid treatment.

Each of these diagnoses requires careful consideration of the patient's clinical presentation, laboratory findings, and imaging studies to determine the most appropriate course of action.