A 45-year-old man came to the hematologist with complaints of general weakness, elevated body temperature, excessive sweating, enlarged cervical lymphnodes. Objectively, his body temperature is 375°C, the skin is pale and dry, the posterior cervical lymph nodes are dense and elastic, up to 2 cm in diameter, mobile. Hepatosplenomegaly was detected. What examination is necessary to determine the scope of the pathologic process?