A 52-year-old male presents with gradually enlarging neck masses over 3 months and intermittent fever with pruritus for 1 month. On examination: temperature 38.9°C, multiple pea-to-bean-sized enlarged lymph nodes in bilateral cervical, supraclavicular, and left axillary regions, some matted, firm consistency, no tenderness. Left cervical lymph node biopsy confirms Hodgkin lymphoma. The most common initial symptom in such patients is: