Systemic Lupus Erythematosus (SLE): This autoimmune disease can cause a wide range of symptoms including lymphadenopathy, rash (characteristically a malar rash), pleural effusions, and ascites due to its potential to affect multiple organ systems.

Lymphoma: Both Hodgkin's and non-Hodgkin's lymphoma can present with lymphadenopathy, and systemic symptoms can include skin rashes. Pleural effusions and ascites can occur due to direct involvement of these spaces by the lymphoma.
Tuberculosis (TB): TB can cause lymphadenopathy, and in its disseminated form, can lead to pleural effusions and ascites. A rash, although less common, can also be a manifestation of TB.
Sarcoidosis: This condition can lead to lymphadenopathy, skin rashes (such as erythema nodosum), and can affect the lungs leading to pleural effusions. Ascites is less common but can occur in abdominal sarcoidosis.

Malignancy (e.g., Metastatic Cancer): Certain cancers, especially those originating from the breast, lung, or abdomen, can metastasize to lymph nodes, cause pleural effusions, and lead to ascites. A rash could be related to the cancer itself or to a paraneoplastic syndrome.
Infectious Endocarditis: Although less directly linked to all these symptoms, infectious endocarditis can cause systemic emboli leading to lymphadenopathy, skin rashes (e.g., Janeway lesions), and potentially pleural effusions and ascites if there is significant cardiac dysfunction.
HIV/AIDS: Given the immunocompromised state, patients with HIV/AIDS can present with a variety of opportunistic infections and malignancies that could explain these symptoms.

Kikuchi-Fujimoto Disease: A rare, self-limiting condition that primarily affects the lymph nodes in the neck, causing lymphadenopathy, and can be accompanied by a rash. While pleural effusions and ascites are not typical, the disease's rarity and potential for systemic symptoms warrant its consideration.
Whipple's Disease: A systemic bacterial infection that can cause lymphadenopathy, skin rash, and involvement of other systems leading to pleural effusions and ascites, although these are less common manifestations.
Castleman Disease: A rare disorder that involves an overgrowth of cells in the body's lymph nodes, which can lead to lymphadenopathy, and systemic symptoms including rash, pleural effusions, and ascites, particularly in the multicentric form.