Chronic Interstitial Cystitis: This condition is characterized by chronic inflammation of the bladder, leading to symptoms such as dysuria and flank pain, without evidence of infection or stones. The negative infection and stone tests support this diagnosis.

Overactive Bladder: This condition can cause dysuria and flank pain due to the frequent and urgent need to urinate, which may be misinterpreted as pain.
Bladder Outlet Obstruction: Obstruction of the bladder outlet, often due to benign prostatic hyperplasia in men or urethral stricture, can cause dysuria and flank pain.
Urethral Syndrome: This condition is characterized by symptoms of dysuria, frequency, and urgency, without evidence of infection or other obvious causes.

Renal Cell Carcinoma: Although rare, renal cell carcinoma can present with flank pain and dysuria, making it essential to consider in the differential diagnosis to avoid missing a potentially life-threatening condition.
Ureteral Cancer: Similar to renal cell carcinoma, ureteral cancer is rare but can cause flank pain and dysuria, emphasizing the need for thorough evaluation.
Vasculitis (e.g., ANCA-associated vasculitis): Certain types of vasculitis can affect the kidneys and urinary tract, leading to symptoms such as flank pain and dysuria, and require prompt diagnosis and treatment to prevent serious complications.

Eosinophilic Cystitis: A rare condition characterized by eosinophilic infiltration of the bladder wall, leading to symptoms such as dysuria and flank pain.
Malacoplakia: A rare inflammatory condition that can affect the urinary tract, causing symptoms such as dysuria and flank pain.
Sarcoidosis involving the urinary tract: Sarcoidosis is a systemic disease that can rarely involve the urinary tract, leading to symptoms such as dysuria and flank pain.