Enlarged lymph nodes or “glands” are the most common symptom of lymphoma. Dogs still may feel normal at this point in the disease or they may have vague symptoms. Nonspecific signs may include: 1  Distended abdomen. 2  Lethargy.3  Coughing. 4  Shortness of breath. 5  Fever.6  Poor appetite.nlarged lymph nodes or “glands” are the most common symptom of lymphoma. Dogs still may feel normal at this point in the disease or they may have vague symptoms. Nonspecific signs may include: 1  Distended abdomen. 2  Lethargy.