Differential Diagnosis
- Single most likely diagnosis
- Psoriatic arthritis: The patient's chronic rash on elbows and knees, which is likely psoriasis, combined with back pain that worsens in the morning and tender sacroiliac joints, points towards psoriatic arthritis. The absence of rheumatoid factor and ANCA also supports this diagnosis, as psoriatic arthritis can be seronegative.
- Other Likely diagnoses
- Ankylosing spondylosis: The patient's back pain worsening in the morning and tender sacroiliac joints could also suggest ankylosing spondylosis, a form of spondyloarthritis. However, the presence of a chronic rash on elbows and knees is more indicative of psoriatic arthritis.
- Reactive arthritis: This condition is also a form of spondyloarthritis and could present with similar symptoms, including back pain and sacroiliac joint tenderness. However, reactive arthritis typically follows a gastrointestinal or genitourinary infection, which is not mentioned in the patient's history.
- Do Not Miss
- Inflammatory bowel disease-associated arthritis: Although less likely, inflammatory bowel disease (IBD) such as Crohn's disease or ulcerative colitis can cause arthritis, including sacroiliitis and spondylitis, similar to the patient's symptoms. Missing this diagnosis could lead to untreated IBD, which can have serious complications.
- Osteomyelitis or discitis: Infectious causes of back pain, such as osteomyelitis or discitis, are less likely given the chronic nature of the patient's symptoms and the absence of fever or other signs of infection. However, these conditions can be severe and require prompt treatment.
- Rare diagnoses
- Enteropathic arthritis: A rare condition associated with IBD, which can cause arthritis, including axial involvement.
- Spondyloarthritis associated with other conditions: Such as juvenile idiopathic arthritis or undifferentiated spondyloarthritis, which could present with similar symptoms but are less common or have different underlying causes.