Differential Diagnosis for 40-year-old Male Presenting with Generalized Tonic-Clonic Seizure and Ventricular Tachycardia

• Single Most Likely Diagnosis:
  • Electrolyte Imbalance (e.g., Hypokalemia, Hypomagnesemia): Despite the normal metabolic panel, electrolyte imbalances can sometimes be missed or develop rapidly. The recent onset of fatigue could be related to an underlying metabolic issue, and both seizures and ventricular tachycardia can be precipitated by significant electrolyte disturbances.
• Other Likely Diagnoses:
  • Drug-Induced Toxicity: Given the patient's history of depression, there's a possibility of overdose or toxicity from antidepressants, which can cause both seizures and cardiac arrhythmias.
  • Infection: Although the CBC is normal, certain infections (e.g., CNS infections) can present with seizures and may not always have an immediately apparent abnormality in the CBC.
  • Thyroid Storm: This condition can cause seizures, arrhythmias, and may not always have a clear preceding history of thyroid disease.
• Do Not Miss Diagnoses:
  • Cardiac Ischemia/Myocardial Infarction: Although the patient has no known history of cardiac problems and a recent normal ECG, cardiac ischemia can occur without warning and can cause both ventricular tachycardia and seizures.
  • Pulmonary Embolism: A large pulmonary embolism can cause sudden cardiac strain leading to arrhythmias and decreased cerebral perfusion leading to seizures.
  • Subarachnoid Hemorrhage or Other Intracranial Bleeds: These can cause seizures and, through various mechanisms (e.g., catecholamine surge), lead to cardiac arrhythmias.
• Rare Diagnoses:
  • Channelopathies (e.g., Brugada Syndrome, Long QT Syndrome): These are genetic conditions that affect the heart's electrical system and can cause life-threatening arrhythmias. They might not have been previously diagnosed and could explain the ventricular tachycardia.
  • Mitochondrial Myopathies: Rare conditions that affect the mitochondria and can lead to a variety of systemic symptoms including seizures and cardiac arrhythmias.
  • Neurodegenerative Disorders with Systemic Involvement: Certain rare neurodegenerative disorders can have systemic manifestations including cardiac and neurological symptoms.