Feline low-grade alimentary lymphoma: how common is it?

Low-grade alimentary lymphoma (LGAL) requires histological assessment of biopsies for diagnosis whereas intermediate- (IGAL) and high-grade (HGAL) alimentary lymphoma (AL) can be diagnosed by cytology of intestinal or mesenteric lymph node aspirates. Assessment of the relative frequency of subtypes of AL using histology alone may be skewed towards an increased frequency of LGAL as cases of IGAL or HGAL diagnosed cytologically may not progress to biopsy. We investigated the relative prevalence of AL subtypes diagnosed by both histopathology and cytology among primary accession cases across Australia during a 5-year period. Clinicopathological features of LGAL were compared with those of IGAL/HGAL. Fifty-three cases of AL were identified, including 30 diagnosed by histology (15 LGAL, 13 HGAL, two IGAL) and 23 IGAL/HGAL diagnosed by cytology. LGAL cases comprised 50% of histological diagnoses, but only 28% of all AL. A palpable abdominal mass was more common in IGAL/HGAL (43%) than in LGAL (7%) [odds ratio (OR) 7.6, P = 0.01]. Anaemia was more common in IGAL/HGAL (41%) compared with LGAL (7%) (OR 9.6, P = 0.02). On abdominal ultrasound, a gastrointestinal mural mass was visualised in 41% of IGAL/HGAL and 0% of LGAL (P = 0.01). Where a detailed abdominal ultrasound report was provided, gastric/intestinal wall thickening was the most commonly reported abnormality (82%). In cats with intestinal thickening, a loss of normal layering was more common (P = 0.02) in cats with IGAL/HGAL (71%) compared with those with LGAL (20%). The relative prevalence of LGAL was lower when cases diagnosed by cytology were included in addition to those diagnosed by histology in the study population. The relative frequency with which LGAL is diagnosed has increased since initial reports from this region. A number of significant clinicopathological findings are useful to distinguish LGAL from IGAL/HGAL.