A 77-year-old female presents to the emergency department after their daughter found them on the floor in their home. The patient is unsure how long she was on the floor, but she said her arms and legs feel sore. A urine dipstick is performed, which shows 3+ blood. Her urine is also dark brown in colour.

What is the most likely diagnosis?

Options:
explanation: Acute interstitial nephritis is a hypersensitivity reaction causing inflammation of the interstitium of the kidneys. This presents with a delayed presentation of fever, rash and acute kidney injury. It is typically a drug reaction with common causes including penicillin antibiotics, NSAIDs and proton pump inhibitors. The urine dipstick results typically found in acute interstitial nephritis include pyuria, but not haematuria. As this patient has presented with a dipstick positive for blood in the context of a long lie, rhabdomyolysis is the more likely diagnosis
name: Acute interstitial nephritis
label: e
answer: no
explanation: Dehydration can be a cause of pre-renal acute kidney injury, particularly in those who are elderly or have other risk factors such as dementia. In this case, this patient presents with myalgia, a urine dipstick positive for blood and changes to the colour of their urine. These are not features of dehydration and suggest a different cause. Therefore, rhabdomyolysis is the more likely differential
name: Dehydration
label: b
answer: no
explanation: Glomerulonephritis is a diverse group of conditions that can be separated broadly into nephrotic syndrome and nephritic syndrome. Nephrotic presents differently to this case, typically with a triad of oedema, hypercholesterolaemia and hypoalbuminaemia. It is diagnosed based on a high protein level in the urine. Nephritic syndrome causes blood in the urine; however, like the vast majority of glomerular disorders, it will also cause proteinuria. This is because glomerular damage causes a leak of protein and blood. As this patient did not have a urine dipstick positive for protein, glomerulonephritis is unlikely to be the cause of this presentation
name: Glomerulonephritis
label: d
answer: no
explanation: Rhabdomyolysis is a condition characterised by skeletal muscle breakdown. There are several typical features of rhabdomyolysis in this question. This is an elderly patient presenting after a long lie, which is a typical cause of rhabdomyolysis. The patient is complaining of soreness in their arms and legs, which may be myalgia associated with rhabdomyolysis (the breakdown of muscle tissue). Breakdown of skeletal muscle tissue releases myoglobin into the systemic circulation, which is associated with renal complications, including acute kidney injury. This explains the colour of this patient's urine, with urine in rhabdomyolysis typically described as being "cola coloured". The 3+ blood is actually a false positive reading for haemoglobin, as it is actually myoglobin responsible for this result
name: Rhabdomyolysis
label: a
answer: yes
explanation: Stones can present with a dipstick positive for blood. However, they will also probably present with colicky abdominal pain, whereas this patient presents with generalised pain affecting their arms and legs. These features, in combination with a long lie, make a diagnosis of rhabdomyolysis more likely
name: Renal calculi
label: c
answer: no

Correct answer: a