Differential Diagnosis for a 31-year-old Female with a Lump on the Right Side of Her Throat

Single Most Likely Diagnosis

• Reactive lymphadenopathy: Given her history of rheumatoid arthritis (RA) and recent sore throat, a reactive lymph node enlargement due to inflammation or infection is the most plausible explanation. The lack of pain and the gradual onset also support this diagnosis.

Other Likely Diagnoses

• Tonsillar abscess or peritonsillar abscess: Although she denies pain, the presence of a lump and a history of sore throat could suggest a localized infection. However, the absence of significant pain makes this less likely.
• RA-related lymphadenopathy: Rheumatoid arthritis can cause lymph node enlargement, but this is less common and usually associated with more systemic symptoms or active disease.
• Viral pharyngitis: The symptoms of a sore throat and a lump could be due to a viral infection, with the lymph node reacting to the infection.

Do Not Miss Diagnoses

• Lymphoma: Although rare, lymphoma can present with painless lymphadenopathy. Given her age and the presence of a lump without significant pain, it's crucial to consider this diagnosis to ensure timely investigation and treatment if necessary.
• Tuberculosis (TB): TB can cause lymphadenopathy, especially in the context of immunosuppression (e.g., from RA treatments). The lack of systemic symptoms does not rule out TB.
• Metastatic cancer: Although unlikely in a young adult without a known primary cancer, any new lump, especially one that is painless and persistent, warrants consideration of malignancy.

Rare Diagnoses

• Sarcoidosis: This condition can cause lymphadenopathy but is less common and usually presents with systemic symptoms or involvement of other organs.
• Kikuchi-Fujimoto disease: A rare, self-limiting condition that causes lymphadenopathy, typically in young women, but it often presents with systemic symptoms like fever.
• Castleman disease: A rare disorder that can cause lymphadenopathy, but it's more commonly associated with systemic symptoms or found incidentally.

Each of these diagnoses should be considered in the context of her full medical history, physical examination, and appropriate diagnostic tests to determine the cause of the lump on her throat.