Differential Diagnosis
The patient's presentation with chronic lower back pain and abnormal bone marrow signal involving the L2 vertebral body, along with the progression of the abnormality and involvement of adjacent vertebrae, suggests an underlying inflammatory or malignant process. The following differential diagnoses are considered:
- Single most likely diagnosis
- Ankylosing Spondylitis with Anderson Lesion: The patient's imaging findings, including the abnormal bone marrow signal, endplate changes, and sclerosis of the L2 vertebral body, are consistent with an inflammatory aetiology. The presence of a fused left sacroiliac joint on the previous CT scan and the progression of the abnormality over time support this diagnosis. The Anderson lesion, a type of inflammatory lesion associated with ankylosing spondylitis, can present with similar imaging features.
- Other Likely diagnoses
- Lymphoma: Although the imaging findings are not typical for underlying malignancy, lymphoma cannot be excluded as a differential diagnosis. The patient's age and lack of systemic symptoms make this diagnosis less likely, but it should still be considered.
- Infectious Spondylodiscitis: The patient's positive QuantiFERON test and the presence of a small paravertebral collection on the MRI scan raise the possibility of an infectious aetiology. However, the lack of systemic symptoms and the normal inflammatory markers make this diagnosis less likely.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Metastatic Disease: Although the imaging findings are not typical for metastatic disease, it is essential to exclude this diagnosis due to its potential severity. The patient's history of a melanocytic naevus and the abnormal bone marrow signal warrant further investigation to rule out metastatic disease.
- Multiple Myeloma: The patient's abnormal bone marrow signal and the presence of a monoclonal gammopathy (although not detected on the serum free light chain test) make multiple myeloma a diagnosis that should not be missed.
- Rare diagnoses
- Amyloidosis: The patient's imaging findings, including the abnormal bone marrow signal and sclerosis of the L2 vertebral body, can be seen in amyloidosis. Although this diagnosis is rare, it should be considered and excluded due to its potential severity.
- Tuberculosis: Although active TB has been excluded, it is essential to consider this diagnosis due to its potential severity and the patient's positive QuantiFERON test. However, the lack of systemic symptoms and the normal inflammatory markers make this diagnosis less likely.