Differential Diagnosis for Prolonged QTc Interval with Dizziness and Left-Sided Numbness

Single Most Likely Diagnosis

• Torsades de Pointes: This is a type of abnormal heart rhythm that can be life-threatening. It is often associated with a prolonged QT interval and can cause symptoms such as dizziness, syncope, and even sudden death. The left-sided numbness could be related to decreased cerebral perfusion during episodes of arrhythmia.

Other Likely Diagnoses

• Stroke or Transient Ischemic Attack (TIA): Although the primary concern is cardiac due to the prolonged QTc interval, the symptom of left-sided numbness is highly suggestive of a neurological event. A stroke or TIA could explain the numbness, and dizziness could be a related symptom.
• Seizure Disorder: Seizures can cause both dizziness and numbness, and in some cases, cardiac arrhythmias can precipitate seizures. The prolonged QTc interval might be a contributing factor or an unrelated finding.
• Vasovagal Syncope: This condition can cause dizziness and fainting spells, often triggered by stress or certain medications. While it doesn't directly explain the left-sided numbness, it's a common cause of dizziness and could be considered if the numbness is transient or not clearly related to the cardiac issue.

Do Not Miss Diagnoses

• Cardiac Arrest: Although not a diagnosis per se, cardiac arrest is a potential outcome of untreated torsades de pointes or other severe cardiac arrhythmias. Immediate recognition and intervention are crucial.
• Myocardial Infarction: A heart attack can cause arrhythmias, including those leading to a prolonged QT interval, and can also cause dizziness and numbness due to decreased cardiac output or embolic phenomena.
• Subarachnoid Hemorrhage: This is a severe condition that can cause sudden onset of headache, dizziness, and sometimes focal neurological deficits like numbness. It's less likely but critical not to miss due to its high mortality rate.

Rare Diagnoses

• Mitochondrial Myopathies: Certain mitochondrial disorders can affect both the heart (leading to QT prolongation) and the nervous system (causing numbness and other neurological symptoms).
• Fabry Disease: A genetic disorder that can cause cardiac arrhythmias, including QT prolongation, and neurological symptoms such as numbness due to small fiber neuropathy.
• Arnold-Chiari Malformation: A structural defect in the cerebellum that can cause a variety of neurological symptoms, including numbness, and potentially contribute to arrhythmias through autonomic dysfunction.