Rheumatoid Arthritis (RA): Despite the rheumatoid factor being within the normal range, RA is still a strong consideration due to the presence of swan neck deformity, a common feature in RA, and symptoms of inflammatory arthritis. Many patients with RA can have negative rheumatoid factor, especially early in the disease course.

Psoriatic Arthritis (PsA): This condition can present with inflammatory arthritis and deformities similar to RA. The absence of rheumatoid factor does not rule out PsA, and the presence of psoriasis or a family history of psoriasis would support this diagnosis.
Lupus Arthritis: Systemic Lupus Erythematosus (SLE) can cause inflammatory arthritis and may present with a high ESR. Although rheumatoid factor can be positive in SLE, it is not a requirement for diagnosis.
Seronegative Arthritis: This term encompasses a group of conditions (including ankylosing spondylitis, reactive arthritis, and the arthritis associated with inflammatory bowel disease) that are characterized by inflammatory arthritis without the presence of rheumatoid factor.

Septic Arthritis: Although less likely given the chronic nature suggested by deformity, septic arthritis is a medical emergency that requires prompt diagnosis and treatment. A high ESR and symptoms of inflammatory arthritis could be present, and the absence of rheumatoid factor does not rule out this condition.
Lyme Arthritis: Caused by Borrelia burgdorferi, Lyme disease can lead to inflammatory arthritis, particularly in endemic areas. The diagnosis is critical due to the potential for serious complications if left untreated.
Crystal Arthropathies (Gout or Pseudogout): While these conditions typically present with acute, episodic arthritis, chronic forms can mimic inflammatory arthritis. A high ESR can be seen in both conditions, and the absence of rheumatoid factor does not rule out crystal arthropathies.

Relapsing Polychondritis: A rare autoimmune disorder characterized by recurrent episodes of cartilaginous inflammation, which can lead to deformities and arthritis.
Multicentric Reticulohistiocytosis: A rare condition that can cause inflammatory arthritis and characteristic skin lesions, leading to deformities similar to those seen in RA.
Hemochromatosis Arthropathy: A rare genetic disorder leading to iron overload, which can cause a form of arthritis that may mimic inflammatory arthritis, although it typically presents with a more chronic and progressive course.