Adult-Onset Still's Disease (AOSD): Despite initial normal ferritin levels, the recurrent fever, polyarthralgia, and inflammatory changes on biopsy are consistent with AOSD. The absence of hepatosplenomegaly and leukocytosis does not rule out this diagnosis, as these features can be variable.

Systemic Lupus Erythematosus (SLE): Although ANA, anti-ENA, and dsDNA are negative, SLE can present with a wide range of symptoms, including polyarthralgia, fever, and oral ulcers. The presence of immune complex deposition on kidney biopsy also suggests an autoimmune process.
Relapsing Polychondritis: Although the patient denies redness over auricular cartilages and dorsum of nose, this diagnosis should be considered due to the presence of nasal ulcer with crusting and minimal blood.
Sjögren's Syndrome: The presence of oral ulcers and recurrent sore throat could suggest Sjögren's syndrome, although other typical features such as dry eyes and mouth are not mentioned.

Infectious Endocarditis: Although extensive evaluation for infection has been unremarkable, infectious endocarditis can present with fever, joint pain, and embolic phenomena (e.g., petechial rash). It is essential to consider this diagnosis due to its high mortality if left untreated.
Lymphoma: The presence of recurrent fever, night sweats, and weight loss (not mentioned but possible) could suggest lymphoma. Although CT chest shows no lymphadenopathy, a thorough evaluation for lymphoma is crucial.

Multicentric Castleman's Disease: This rare disorder can present with fever, polyarthralgia, and lymphadenopathy (although not present in this case). The presence of immune complex deposition on kidney biopsy could also suggest this diagnosis.
TNF Receptor-Associated Periodic Syndrome (TRAPS): This autosomal dominant disorder can present with recurrent fever, abdominal pain, and arthralgia. Although the patient's symptoms do not perfectly align with TRAPS, it is essential to consider this diagnosis due to its rarity and potential for significant morbidity.