Rheumatoid Arthritis (RA): This is a common autoimmune disorder that often presents with joint stiffness, particularly in the mornings, and can be associated with lymphadenopathy due to the systemic nature of the disease.

Lupus: Systemic Lupus Erythematosus (SLE) is another autoimmune disease that can cause joint stiffness and lymphadenopathy, along with a variety of other systemic symptoms.
Psoriatic Arthritis: This condition combines the swollen, scaly skin of psoriasis with joint pain and arthritis, and can also include lymphadenopathy.
Lymphoma: Both Hodgkin's and non-Hodgkin's lymphoma can present with lymphadenopathy, and some patients may experience joint stiffness due to bone marrow involvement or paraneoplastic syndromes.

Septic Arthritis: Although less common, septic arthritis is a medical emergency that requires prompt diagnosis and treatment. It can present with acute joint stiffness and swelling, and systemic symptoms including fever and lymphadenopathy.
Tuberculosis: TB can affect the joints (ostearticular TB) and lymph nodes, presenting with chronic joint stiffness and lymphadenopathy. It's crucial to consider TB, especially in endemic areas or in individuals with risk factors.
HIV: Human Immunodeficiency Virus infection can lead to a variety of musculoskeletal symptoms, including joint stiffness and lymphadenopathy, due to the infection itself or opportunistic infections.

Sarcoidosis: This is a systemic granulomatous disease that can affect multiple organs, including the joints and lymph nodes, leading to stiffness and lymphadenopathy.
Whipple's Disease: A rare, systemic bacterial infection that can cause joint stiffness, lymphadenopathy, and a range of other symptoms including gastrointestinal and neurological manifestations.
Castleman Disease: A rare disorder that involves an overgrowth of cells in the body's lymph nodes, which can lead to lymphadenopathy and may be associated with joint symptoms in some cases.