Differential Diagnosis for Painful Lumps on Arms and Legs

Single Most Likely Diagnosis

• Pancreatic Panniculitis: This condition is characterized by painful subcutaneous nodules, often associated with pancreatic disease. The location and mobility of the lumps, along with their deep position in the fat tissue, are consistent with this diagnosis. The fact that they are becoming more painful each day also aligns with the natural progression of pancreatic panniculitis.

Other Likely Diagnoses

• Erythema Nodosum: A condition that presents with painful, erythematous nodules, typically on the lower extremities. While the locations mentioned are not exclusive to erythema nodosum, the painful nature and mobility of the lumps could fit this diagnosis.
• Subcutaneous Fat Necrosis: This condition can cause painful lumps due to the necrosis of subcutaneous fat. It can occur post-trauma or in the context of certain diseases, and the description of deep, painful, and mobile lumps could be consistent with this diagnosis.
• Rheumatoid Nodules: Associated with rheumatoid arthritis, these nodules can be found on the extremities and can be painful. Their presence in areas like the elbows, knees, and fingers could suggest this diagnosis, especially if there are other symptoms of rheumatoid arthritis.

Do Not Miss Diagnoses

• Septic Arthritis or Osteomyelitis: Although less likely given the description of mobile, subcutaneous lumps, it's crucial not to miss infections of the bone or joint, as they can be severe and require immediate treatment. The presence of pain and the specific locations (e.g., near joints) necessitate consideration of these conditions.
• Malignancy (e.g., Metastatic Disease): While rare, subcutaneous metastases can present as painful lumps. Given the potential severity of cancer, it's essential to consider this in the differential diagnosis, especially if there's a known history of cancer.

Rare Diagnoses

• Weber-Christian Disease: A rare inflammatory disorder of the fatty tissues under the skin, characterized by recurring episodes of painful inflammation. The description of painful lumps deep in the fat tissue could fit this diagnosis, although it is much less common.
• Alpha-1 Antitrypsin Deficiency Panniculitis: A rare condition associated with deficiency of alpha-1 antitrypsin, leading to painful subcutaneous nodules. This diagnosis would be considered if other more common causes are ruled out and there's a relevant family or personal history.