Differential Diagnosis
- Single most likely diagnosis
- B. Acute osteomyelitis: This is the most likely diagnosis given the patient's symptoms of acute onset pain and tenderness in the lower back, the presence of a paraspinal fluid collection on MRI, and the increased signal intensity of the adjacent vertebral bone marrow on T1-weighted, post-contrast images. The patient's recent hospitalization for MRSA bacteremia and the failure of blood cultures to clear despite antibiotic treatment suggest hematogenous spread of the infection to the spine.
- Other Likely diagnoses
- D. Infected sacral decubitus ulcer: Although the skin is intact, the presence of nonblanching erythema over the lower back and sacrum could suggest an early or deep decubitus ulcer that has become infected, potentially with MRSA. However, the MRI findings pointing towards vertebral bone marrow involvement make this less likely than acute osteomyelitis.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Epidural abscess: This is a medical emergency that can present with back pain, fever, and neurological deficits. Although the MRI shows a paraspinal fluid collection, an epidural abscess would typically require urgent surgical intervention. The absence of neurological symptoms and the specific location of the fluid collection make this less likely, but it cannot be entirely ruled out without further evaluation.
- Spinal epidural hematoma: Although less likely given the clinical context, any new onset back pain in a patient with potential coagulopathy (e.g., from dialysis) or those on anticoagulation should prompt consideration of a spinal epidural hematoma, which is a surgical emergency.
- Rare diagnoses
- Chronic osteomyelitis (A): This would be less likely given the acute onset of symptoms and the presence of systemic infection (MRSA bacteremia). Chronic osteomyelitis typically presents with a longer history of symptoms and may not always have an identifiable source of infection.
- Charcot spinal arthropathy (C): This condition is associated with diabetic neuropathy and can lead to destructive changes in the spine. However, it does not typically present with acute onset pain and fever, nor with the specific MRI findings described in this case.