GENERAL CONSIDERATIONS
+ General Considerations
- Visceral involvement reported in up to 50% of feline mastocytic MCT with the spleen the most common site for visceral MCT, but other sites include mediastinum (with pleural effusion), lymph node, and intestines
- Splenic or lymphoreticular form is common and accounts for 15% of all splenic pathology in cats
- 3 forms of splenic MCT: smooth, diffuse, and nodular
- Dissemination and metastasis is more common in visceral MCT with splenic MCT disseminating to the liver (90%), visceral lymph nodes (73%), bone marrow (23%-40%), lung (20%), and intestine (17%)
- Pleural effusion occurs in 15% of cats with visceral MCT
- Peritoneal and pleural effusion rich in mast cells and eosinophils in up to 33% cats
- Cats with primary visceral MCT rarely have cutaneous involvement, but splenic MCT is reported in 18% of cats with cutaneous MCT
- DDx: LSA, myeloproliferative disease, accessory spleen, HSA, hyperplastic nodules, and splenitis
+ Clinical Signs
Systemic illness with visceral or systemic forms:
- Depression
- Anorexia
- Weight loss
- Intermittent vomiting
+ Diagnosis
- Splenomegaly ± peritoneal effusion for splenic MCT
- Abdominal mass with diarrhea and possibly pyrexia in intestinal MCT
- Mast degranulation is usually episodic with systemic mastocytosis and clinical signs include GI ulceration, uncontrollable hemorrhage, altered smooth muscle tone, hypotensive shock, and respiratory distress
- Respiratory distress can also be caused by pleural effusion or anemia which is present in up to 33% of cats
- FNA of cutaneous mass, spleen, intestinal mass, or from pleural or peritoneal fluid: granules stain blue with Giemsa and purple with toluidine blue and appear more eosinophilic with hematoxylin and eosin stains
- Tissue biopsy and histology required for diagnosis of histiocytic MCT
- Disseminated disease: hematology, serum biochemistry, buffy coat smear, bone marrow aspirate, and coagulation profile
- Anemia (33%) common in the splenic but not intestinal form due to increased splenic sequestration, red blood cell coating with antibodies, and endocytosis of red blood cells by mast cells
- Cats with systemic mastocytosis will have eosinophilia, basophilia and peripheral mastocytosis (50%)
- Mast cells can account for up to 25% of white blood cells in cats
- Coagulation abnormalities reported in 90% of cats with splenic MCT, but rarely clinically significant
- Methylated metabolites of histamine in urine may be a valuable diagnostic technique for mastocytosis
+ Treatment
- Surgery: splenectomy for splenic MCT
- Effectiveness of adjunctive therapy unknown
- Combination chemotherapy protocols using prednisone, vincristine, cyclophosphamide, and methotrexate have not offered a survival advantage over surgery alone
+ Prognosis
- MST 12-19 months due to reduction of splenic suppressor cell activity allowing immune system control (hence corticosteroids are controversial in feline MCT)
- Peripheral mastocytosis will decrease but rarely resolve, however, increase can be marker for progression
- Poor prognostic factors include anorexia, significant weight loss, and male