Differential Diagnosis

The patient's symptoms of decreased appetite, weakness, malaise, tremulousness, and oliguria (not having urinated since yesterday) suggest a serious underlying condition. Here's a categorized differential diagnosis:

• Single most likely diagnosis

  • Rhabdomyolysis: This condition, characterized by the breakdown of muscle tissue, is likely given the patient's history of intense daily workouts and the use of creatine supplements. The symptoms of weakness, malaise, and particularly the lack of urination, which could indicate acute kidney injury (a complication of rhabdomyolysis), support this diagnosis.

• Other Likely diagnoses

  • Dehydration: Given the patient's decreased appetite and lack of urination, dehydration is a plausible diagnosis, potentially exacerbated by the patient's workout regimen and supplement use.
  • Electrolyte Imbalance: The use of supplements like creatine can lead to electrolyte imbalances, especially if the patient is not adequately hydrated. This could contribute to feelings of weakness and malaise.
  • Viral Illness: A viral infection could explain the patient's symptoms of decreased appetite, weakness, and malaise, although the specific symptom of not having urinated since yesterday might be less commonly associated with viral illnesses unless they lead to severe dehydration.

• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)

  • Acute Kidney Injury (AKI): While this could be a consequence of rhabdomyolysis, it's crucial to identify and treat promptly to prevent long-term kidney damage.
  • Heat Stroke: Although the patient works out daily, if these workouts are intense and in high temperatures without adequate hydration, heat stroke could be a life-threatening condition that needs immediate attention.
  • Sepsis: Any infection that leads to sepsis can present with non-specific symptoms such as weakness and malaise. Early recognition and treatment of sepsis are critical.

• Rare diagnoses

  • Thyrotoxic Crisis: Although less likely, this condition can present with tremulousness, weakness, and potentially altered mental status. It's a medical emergency that requires prompt diagnosis and treatment.
  • Adrenal Insufficiency: This could explain the patient's weakness and malaise, especially if there's a history of steroid use (which might not be immediately apparent, including topical or injected forms).
  • Guillain-Barré Syndrome: An autoimmune disorder that could lead to weakness and potentially autonomic dysfunction, although the lack of urination might not be an initial presenting symptom.