The lesion in this syndrome is actually a rapidly growing thymic mass which compresses the lungs. Less commonly, extensive hepatic infiltration by neoplastic lymphocytes may result in marked hepatic enzyme increases and icterus suggesting fulminant liver disease, and so on. Lymphoblastic lymphosarcoma should always be ruled out when dealing with any serious illness in young ferrets. Finally, leukemic forms, in which neoplastic lymphocytes circulate within the peripheral blood, may be seen in the latter stages of either form, but are generally uncommon. Lymphosarcoma in many cases is not an easy diagnosis.
Definitive diagnosis requires interpretation of a lymph node aspirate or biopsy.
While the presence of a monomorphic population of immature lymphocytes on a lymph node aspirate is highly suggestive of this disease, the opinion of a pathologist with ferret experience should be sought in all cases. Alternatively, a diagnosis may be made on biopsies of visceral organs in animals with disseminated disease, with the spleen probably yielding the highest number of positive aspirates or biopsies. Over the last few years, a disturbing trend in diagnosis of this disease has been emerging - the interpretation of elevated lymphocyte counts as evidence of lymphosarcoma in the ferret. While many cases of lymphosarcoma may exhibit a lymphocytosis on the CBC, similar changes in the differential may be seen in any number of chronic smoldering infections, most notably gastric Helicobacter mustelae infection. The prudent practitioner requires a diagnosis by aspirate or surgical biopsy before any treatment is started.