Atypical Ankylosing Spondylitis: Symptoms and Diagnosis - Internal Medicine

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Atypical Ankylosing Spondylitis (AS) can be a challenging diagnosis, especially when the classic symptoms and laboratory findings do not align with the typical presentation of the disease. In your case, you are 30 years old, HLA-B27 negative, and have low inflammatory markers (CRP and ESR), which are not typical for classic AS. However, the presence of sacroiliac joint sclerosis on MRI and persistent buttock pain raises the possibility of a variant or atypical form of AS or another inflammatory condition.

Ankylosing Spondylitis is primarily characterized by chronic inflammation of the spine and the sacroiliac joints, leading to pain and stiffness. The disease often presents in young adults, typically between the ages of 15 and 40, and is more common in males. The classic symptoms include:
1. Chronic Lower Back Pain: This pain is often worse at night or in the early morning and improves with movement.

2. Stiffness: Patients often experience stiffness in the lower back and hips, particularly after periods of inactivity.

3. Peripheral Arthritis: In some cases, AS can also affect peripheral joints, such as the hips, knees, and ankles.

In your situation, the MRI findings of sacroiliac joint sclerosis are significant. This finding can indicate inflammation or damage to the joint, which is a hallmark of AS. However, the absence of HLA-B27 positivity and low inflammatory markers complicates the diagnosis. It is important to note that while HLA-B27 is a strong genetic marker associated with AS, not all patients with AS will test positive for it. Approximately 5-10% of patients with AS are HLA-B27 negative.

The treatment you are currently receiving, including medications like Celecoxib (a non-steroidal anti-inflammatory drug) and Salazopyrine (a disease-modifying anti-rheumatic drug), is appropriate for managing inflammation and pain. However, the lack of improvement after several weeks suggests that your condition may not be responding as expected, which could indicate that your diagnosis might need to be re-evaluated.

Given the presence of ankle effusion (swelling), it is essential to consider other potential diagnoses. Conditions such as reactive arthritis, psoriatic arthritis, or even inflammatory bowel disease-associated arthritis could present with similar symptoms and imaging findings. A thorough evaluation by a rheumatologist is crucial to explore these possibilities further.

In terms of next steps, it may be beneficial to consider additional imaging studies, such as a CT scan of the sacroiliac joints, or even a whole-body MRI to assess for other areas of inflammation. Additionally, a referral to a specialist in rheumatology who has experience with atypical presentations of AS or related spondyloarthritis could provide further insights and management options.

In summary, while your symptoms and MRI findings suggest a possible atypical form of Ankylosing Spondylitis, the negative HLA-B27 status and low inflammatory markers indicate that further investigation is warranted. It is essential to continue working closely with your healthcare team to monitor your symptoms, adjust your treatment plan, and explore other potential diagnoses that may explain your condition. Early and accurate diagnosis is key to managing symptoms effectively and improving your quality of life.