Differential Diagnosis for Severe Myalgia, New Onset Peripheral Edema, and Irregularly Irregular Heart Rhythm
Single Most Likely Diagnosis
- Statin-induced myopathy with rhabdomyolysis and subsequent acute kidney injury leading to hyperkalemia and cardiac arrhythmia: The patient stopped statin 3 days ago, which could be a coincidence, but the onset of joint pain (myalgia) is a common side effect of statins. However, the severe nature and the combination with other symptoms suggest a more serious condition like rhabdomyolysis, especially if the patient was on a high dose or had recently started the medication before stopping. The peripheral edema could be due to renal impairment, and the irregularly irregular heart rhythm could be atrial fibrillation, potentially precipitated by hyperkalemia.
Other Likely Diagnoses
- Atrial Fibrillation with Heart Failure: The irregularly irregular heart rhythm is highly suggestive of atrial fibrillation. New onset peripheral edema could indicate heart failure, which could be precipitated by the arrhythmia or could be a separate condition contributing to the patient's symptoms.
- Thyroid Disorder (Hypothyroidism or Hyperthyroidism): Both conditions can cause myalgia, edema (more common in hypothyroidism), and cardiac arrhythmias (atrial fibrillation is more common in hyperthyroidism). The age of the patient and the combination of symptoms make this a plausible diagnosis.
- Electrolyte Imbalance (e.g., Hyperkalemia, Hyponatremia): Electrolyte disturbances can cause muscle weakness, arrhythmias, and in severe cases, rhabdomyolysis. The recent cessation of statin and the onset of symptoms could be unrelated, but an electrolyte imbalance needs to be considered, especially if the patient is on other medications that affect electrolyte levels.
Do Not Miss Diagnoses
- Pulmonary Embolism: While less likely given the combination of symptoms, pulmonary embolism can cause sudden onset of symptoms including arrhythmias and could potentially lead to heart failure, which might explain the edema. It's a diagnosis that cannot be missed due to its high mortality rate.
- Cardiac Tamponade: This is another life-threatening condition that could cause cardiac arrhythmias and peripheral edema due to impaired cardiac filling. It would be less likely without a history of trauma or malignancy but should be considered in the differential due to its urgency.
Rare Diagnoses
- Polymyalgia Rheumatica (PMR): This condition causes severe myalgia, especially in the shoulders and hips, and can be associated with peripheral edema. While it's more common in older adults, the cardiac arrhythmia would be an unusual presenting feature, making this a less likely diagnosis.
- Dermatomyositis: This is an inflammatory muscle disease that can cause myalgia and, less commonly, cardiac arrhythmias. The absence of skin manifestations makes this diagnosis less likely, but it should be considered if other diagnoses are ruled out and muscle enzymes are elevated.