Rheumatoid Arthritis (RA): This is a common autoimmune disorder that can cause fluid collections and inflammation in multiple joints, including the elbows and shoulders, due to its systemic nature and tendency to affect multiple joints symmetrically.

Osteoarthritis (OA): Although OA is more commonly associated with wear and tear of the joint cartilage, it can also lead to fluid accumulation in the affected joints, including the elbows and shoulders, especially in advanced stages.
Trauma or Injury: Direct trauma to the elbow or shoulder can cause fluid collections due to hemorrhage or inflammation. This could be a likely diagnosis if there's a history of recent injury.
Gout or Pseudogout: These are forms of arthritis characterized by sudden, severe attacks of pain, swelling, redness, and tenderness in one or more joints, most often in the big toe, but can also affect elbows and shoulders, leading to fluid collections.

Septic Arthritis: This is a medical emergency where a joint becomes infected, leading to severe pain, swelling, and fluid accumulation. It requires prompt antibiotic treatment to prevent joint destruction and systemic complications.
Lymphoma or Other Malignancies: Although rare, certain types of cancer can cause fluid collections in joints due to metastasis or direct involvement of the joint.
Hemophilia: In patients with hemophilia, even minor trauma can lead to significant bleeding into joints (hemarthrosis), resulting in fluid collections.

Amyloidosis: A condition characterized by the deposition of amyloid (a particular type of protein) in various tissues, which can lead to joint fluid accumulation among other symptoms.
Sarcoidosis: A disease in which abnormal immune cells, called granulomas, form in various parts of the body, including joints, potentially causing fluid collections.
Villonodular Synovitis (PVNS): A rare condition characterized by the overgrowth of the joint lining (synovium), leading to fluid accumulation and joint damage.