Final answer:
The suspected diagnosis is lymphoma, a type of cancer that affects lymphocytes and can cause fatigue, lymphadenopathy, splenomegaly, and isolated lymphocytosis.
Step-by-step explanation:
The suspected diagnosis for the 80-year-old man with fatigue, lymphadenopathy, splenomegaly, and isolated lymphocytosis is lymphoma. Lymphoma is a type of cancer that affects the lymphocytes, which are white blood cells involved in the immune system.Lymphoma can cause enlargement of lymph nodes, leading to lymphadenopathy, as well as enlargement of the spleen, known as splenomegaly. Fatigue is a common symptom of lymphoma, and isolated lymphocytosis refers to an increased number of lymphocytes in the blood.It is important for the patient to undergo further diagnostic tests, such as a biopsy, to confirm the diagnosis and determine the specific type of lymphoma.