Differential Diagnosis for Chronically Declining Kidney Function

The patient's declining kidney function, alongside a history of Sjögren's syndrome and additional symptoms such as frequent pneumonia infections, long-term mildly decreased WBC, and long-term high serum protein, presents a complex clinical picture. The following differential diagnoses are categorized based on their likelihood and potential impact:

• Single Most Likely Diagnosis

  • Sjögren's Syndrome-associated Interstitial Nephritis: This is a common renal manifestation of Sjögren's syndrome. The chronic inflammation associated with Sjögren's can lead to interstitial nephritis, which would explain the decline in kidney function. The patient's existing diagnosis of Sjögren's makes this a highly plausible cause.

• Other Likely Diagnoses

  • Hypertension: Uncontrolled hypertension is a common cause of chronic kidney disease. Even if not previously diagnosed, the development of hypertension could explain the decline in renal function.
  • Diabetes Mellitus: Similar to hypertension, undiagnosed or poorly controlled diabetes can lead to diabetic nephropathy, causing a decline in kidney function over time.
  • Chronic Pyelonephritis: Recurrent or chronic infections of the kidney can lead to scarring and a decline in renal function. This could be a consideration, especially if the patient has a history of urinary tract infections.
  • Analgesic Nephropathy: Long-term use of certain analgesics, such as NSAIDs, can cause chronic kidney damage. Given the patient's Sjögren's syndrome, they might be more likely to use these medications for pain management.

• Do Not Miss Diagnoses

  • Vasculitis (e.g., ANCA-associated vasculitis): Although less common, vasculitis can cause rapid decline in kidney function and is associated with significant morbidity and mortality if not promptly treated.
  • Lupus Nephritis: Given the patient's autoimmune background with Sjögren's, the possibility of systemic lupus erythematosus (SLE) with renal involvement should be considered, as it can cause significant kidney damage.
  • Amyloidosis: This condition, which can be primary or secondary to chronic diseases like Sjögren's, involves the deposition of amyloid proteins in the kidneys, leading to their dysfunction.

• Rare Diagnoses

  • Tubulointerstitial Nephritis and Uveitis Syndrome (TINU): A rare condition characterized by the combination of tubulointerstitial nephritis and uveitis, which could be considered in the differential given the patient's Sjögren's syndrome.
  • Light Chain Deposition Disease: A condition associated with the deposition of light chain immunoglobulins in the kidney, leading to renal dysfunction. This could be a consideration, especially if there's suspicion of a plasma cell dyscrasia.
  • Sarcoidosis: Although rare, sarcoidosis can affect the kidneys and cause a decline in function. It might be considered if other systemic symptoms suggestive of sarcoidosis are present.
  • Multiple Myeloma: Given the patient's long-term high serum protein, multiple myeloma should be considered as it can lead to renal impairment through various mechanisms, including light chain deposition disease.
  • Immunodeficiency: The patient's history of frequent pneumonia infections and mildly decreased WBC count could suggest an underlying immunodeficiency, which might be contributing to the kidney dysfunction, possibly through recurrent infections or an underlying condition affecting both the immune system and the kidneys.