A Prospective, Randomized, Double-Blinded, Placebo-Controlled Study of Human Intravenous Immunoglobulin for the Acute Management of Presumptive Primary Immune-Mediated Thrombocytopenia in Dogs

Background: Immune-mediated thrombocytopenia (IMT) is a common hematologic disorder in dogs. Human intravenous immunoglobulin (hIVIG) may have a beneficial effect in canine IMT.
Hypothesis: A single hIVIG infusion (0.5 g/kg) in dogs with presumed primary IMT (pIMT) is a safe adjunctive emergency treatment to accelerate platelet count recovery and shorten hospitalization time without increasing the cost of patient care.
Animals: Eighteen client-owned dogs with a presumptive diagnosis of pIMT.
Methods: Prospective, randomized, double-blinded, placebo-controlled clinical trial.
Results: There were no identifiable immediate or delayed adverse reactions associated with hIVIG administration over a 6-month period. The median platelet count recovery time for the hIVIG group was 3.5 days (mean ± SD: 3.7 ± 1.3 days; range, 2–7 days) and 7.5 days (mean ± SD: 7.8 ± 3.9 days; range, 3–12 days) for the placebo group. The median duration of hospitalization for hIVIG group was 4 days (mean ± SD: 4.2 ± 0.4 days; range, 2–8 days) and 8 days (mean ± SD: 8.3 ± 0.6 days; range, 4–12 days) for the placebo group. There was no significant difference between groups with respect to expense of initial patient care, whereas significant reduction in platelet count recovery time ( P = .018) and duration of hospitalization ( P = .027) were detected in the hIVIG group.
Conclusions and Clinical Importance: Compared with corticosteroids alone, adjunctive emergency therapy of a single hIVIG infusion was safe and associated with a significant reduction in platelet count recovery time and duration of hospitalization without increasing the expense of medical care in a small group of dogs with presumed pIMT.     

Therapy of Immune Mediated Thrombocytopenia

Fifteen dogs with immune mediated thrombocytopenia (IMT) were studied retrospectively. All dogs had a thrombocyte count below 50,000/microliters when response to therapy was studied. Platelet counts greater than 50,000/microliters were present in all dogs within 2-9 days of initiating medical therapy. Eight dogs experienced a single episode of thrombocytopenia and seven dogs relapsed over the following 5 to 24 months. Clinical parameters from dogs that experienced a single episode of IMT were compared with data from dogs that relapsed to determine whether any information would identify dogs that were prone to relapse. Signalment, severity of thrombocytopenia, and time to achieve a platelet count above 50,000/microliters were found not to differ (P greater than 0.05) between these two groups. Five of the seven dogs with relapsing IMT were splenectomized after 2 to 4 episodes (mean, 2.8 +/- 0.8) of thrombocytopenia over 2 to 14 months. The postoperative progress of these five dogs was followed for 6 to 17 months. Platelet counts were sustained above 200,000/microliters in 4/5 after splenectomy and it was possible to discontinue medical therapy in these dogs. In comparison, the 2 relapsing IMT cases that were not splenectomized continued to require intermittent immunosuppressive therapy. We conclude that signalment and routine pretreatment laboratory test results are not useful in distinguishing dogs with relapsing IMT from those that will experience one episode of IMT. Seemingly, splenectomy is useful in the management of dogs with relapsing IMT.     

Flow cytometric detection of platelet-bound antibody in three horses with immune-mediated thrombocytopenia

Immune-mediated thrombocytopenia (IMT) is a sporadic cause of thrombocytopenia in horses for which it is difficult to establish a definitive diagnosis. In this report, we describe 3 horses with severe thrombocytopenia in which flow cytometric analysis of platelets for surface-bound IgG was used in an attempt to substantiate a provisional diagnosis of IMT. A distinct proportion (4.28%, 5.04%, and 7.95%) of platelets with surface-bound IgG was detected in the 3 thrombocytopenic horses, but not in 6 healthy horses (0.03% to 0.15%) or 6 horses with colic (0.00% to 1.21%). These results, in conjunction with elimination of other potential causes of the thrombocytopenia, established a diagnosis of IMT. The horses were treated with glucocorticoids alone or in combination with azathioprine, and the thrombocytopenia gradually resolved. Flow cytometric detection of platelet-bound IgG was readily performed and may be a useful adjunct for the diagnosis of IMT.     

Platelet-bound antibodies detected by a flow cytometric assay in cats with thrombocytopenia

In cats, primary or secondary immune-mediated thrombocytopenia have rarely been described or characterised. The objective of this study was to determine platelet-bound antibodies (PBA) by a flow cytometric assay in both healthy and thrombocytopenic cats. Direct PBA testing was performed in 42 thrombocytopenic cats (platelet counts 6-179 x 10(9)/l, median 56 x 10(9)/l). Of these 42 cats, 19 had positive PBA test results, 17 of which were considered to have secondary immune-mediated thrombocytopenia (sITP). Underlying diseases included fat necroses (four cases), feline infectious peritonitis (three), feline leukaemia virus (two) or feline immunodeficiency virus (two) infections, lymphoma (two), leukaemia (one), hepatitis (one), pyelonephritis (one), or hyperthyroidism (one). In two cats, no underlying disease was found suggesting a primary immune-mediated thrombocytopenia (pITP). The PBA test was negative in 23 cats diagnosed with varying underlying diseases and in 47 healthy control cats with platelet values within the reference range. Only seven of the 42 cats with thrombocytopenia (platelet count 10-57 x 10(9)/l, median 34 x 10(9)/l) had spontaneous bleeding. This study suggests that immune-mediated destruction of platelets might be an important pathological mechanism for feline thrombocytopenia caused by various underlying diseases. In cats, pITP appears to be rarely diagnosed.     

Application of vincristine-loaded platelet therapy in three dogs with refractory immune-mediated thrombocytopenia

Three dogs presented with refractory immune-mediated thrombocytopenia (IMT). All patients failed to respond to prednisone, which is considered a mainstay of immunosuppressive therapy. Vincristine-loaded platelets (VLPs), which act selectively on mononuclear phagocytes,were introduced. After the VLPs were transfused, two dogs responded quickly withimproved clinical signs while the third dogwith recurrent IMT was euthanized due to its deteriorating condition. This case report describesthe efficacy of VLP therapy in refractory IMT patients.     

Propylthiouracil-associated hemolytic anemia, thrombocytopenia, and antinuclear antibodies in cats with hyperthyroidism

Nine of 105 cats with hyperthyroidism treated with propylthiouracil developed a serious immune-mediated drug reaction during treatment. Adverse clinical signs, which developed after 19 to 37 days (mean, 24.8 days) of propylthiouracil administration, included lethargy, weakness, anorexia, and bleeding diathesis. Physical examination revealed pale mucous membranes, and petechial hemorrhages of the skin and oral cavity. Results of hematologic testing revealed severe anemia and thrombocytopenia. The direct antiglobulin (Coombs') test was positive in all 7 cats evaluated, whereas the serum antinuclear antibody titer was greater than or equal to 1:10 in 5 of the 8 cats tested. In 4 of the cats, treatment included appropriate supportive therapy and cessation of propylthiouracil; in these cats, anemia and thrombocytopenia resolved and Coombs' and antinuclear antibody tests became negative within 2 weeks.     

Idiopathic thrombocytopenic purpura in a cat

An 11-year-old, castrated, male domestic shorthair cat was presented for hematuria and pollakiuria. The cat had a marked thrombocytopenia, and a bone-marrow core biopsy demonstrated megakaryocytic hyperplasia with many megakaryocyte-associated neutrophils (i.e., emperipolesis). On peripheral blood, collected at initial presentation, what appeared to be platelets were noted to be within or adherent to occasional neutrophils. The thrombocytopenia was idiopathic in that no definitive cause could be found. However, platelet concentrations appeared to increase and decrease in response to changes in prednisone and cyclosporine therapy, suggesting a possible immune-mediated pathogenesis. As tests to detect increased feline platelet-associated antibodies are unavailable, immune-mediated thrombocytopenia can only be tentatively diagnosed in cats by exclusion and response to therapy.     

Diagnosis of microthrombocytosis and immune-mediated thrombocytopenia in dogs with thrombocytopenia: 68 cases (1987-1989).

The mean platelet volume (MPV) was evaluated in 68 dogs with thrombocytopenia attributable to various causes. Platelet size was high or low in some dogs. The most clinically useful observation was that low MPV (microthrombocytosis) was a specific indicator of immune-mediated thrombocytopenia (IMT) in these thrombocytopenic dogs. All but one case of microthrombocytosis (MPV less than 5.4 fl) was found in dogs with IMT. Microthrombocytosis was detected in 17 of 31 dogs with IMT and appeared at the onset of the disease. Macrothrombocytosis (MPV greater than 9.4 fl) indicated active thrombopoiesis, but was not unique to any disease category. Macrothrombocytosis was detected in 18 of 31 dogs with IMT, 3 of 17 dogs with disseminated intravascular coagulation, and 3 of 9 dogs with primary bone-marrow disease.     

Immunological anomalies and thrombocytopenia in 117 dogs and cats diagnosed with chronic fatigue syndrome (CFS)

Retrospective analysis of immune dysfunctions found in 55 dogs and 62 cats diagnosed with Chronic Fatigue Syndrome (CFS), revealed leukopenia in 11% of dogs (n = 6) and 22.5% of cats (n = 14), lymphopenia in 14.5% of dogs (n = 8) and 10% of cats (n = 6), hypogammaglobulinaemia in 9% of dogs (n = 5) and 13% of cats (n = 8) and thrombocytopenia in 20% of dogs (n = 11) and 68% of cats (n = 42). All patients had creatine kinase enzyme levels above the normal range (CK = 5-100 IU/L) and carried micrococcus-like organisms on erythrocytes. Blood cultures proved positive for Staphylococcus spp. in 16 cases. After low-dosage arsenic-based therapy (thiacetarsamide sodium) all animals experienced complete clinical remission. Subsequent controls demonstrated immune restoration in 4 representative FIV-FeLV negative cats, previously diagnosed with CFS associated with leukopenia, lymphopenia, hypogammaglobulinaemia and thrombocytopenia. The main conclusion is that a CFS-like disease in dogs and cats, characterised by the common hallmarks of high CK levels, absence of known causes of chronic fatigue in animals and presence of micrococcus-like organisms in the blood, can be associated with humoral and/or cellular immune deficiencies in 9-22.5% of cases and with thrombocytopenia in 20-68% of cases. Considerations are made on the possible role of micrococci in the aetiology of the condition and on the similarities with CFS in humans.     

Transfusion issues in the cancer patient

Blood transfusions are a lifesaving but transient therapy used to correct deficiencies of blood cells and coagulation factors that occur in cancer patients. Anemia can occur in cancer patients as a result of hemolysis, blood loss, or bone marrow failure. The blood component most commonly recommended for the treatment of anemia is packed red blood cells. Coagulation disorders are common with hemangiosarcoma and diffuse hepatic tumors. Fresh frozen plasma is used as a source for replacement coagulation factors for the treatment of disseminated intravascular coagulation or other cancer-associated coagulopathies. Although thrombocytopenia and neutropenia can be the result of bone-marrow failure from tumor infiltration, chemotherapy, or radiation therapy, these platelets and neutrophils are rarely transfused to veterinary cancer patients. Pretransufsion testing consists of blood typing in cats, and cross matching in dogs and cats if the dog has previously been transfused. Cancer patients receiving transfusions should be monitored on a continual basis during and immediately following the transfusion to enable early identification of an adverse event, allowing the transfusion to be discontinued.     

Treatment of severe immune-mediated thrombocytopenia with human IV immunoglobulin in 5 dogs

BACKGROUND: Glucocorticoids with or without other immunotherapy are the initial treatment of choice for dogs with severe immune-mediated thrombocytopenia (IMT). The majority of treated dogs will have improvements in platelet counts within 5 to 7 days of starting therapy, but complications from hemorrhage often occur before a response is seen. Human IV immunoglobulin (hIVIG) blocks Fc receptors on mononuclear phagocytic cells in dogs; it is used in people with idiopathic thrombocytopenic purpura. HYPOTHESIS: The purpose of this study was to describe adverse effects and benefit of hIVIG in addition to conventional immunosuppressive therapy in dogs with severe IMT. ANIMALS: Five client-owned dogs with severe primary IMT. METHODS: Case series. The hospital database was searched for dogs with primary IMT treated with hIVIG. RESULTS: No adverse effects were noted during or after hIVIG infusion in any treated dog. Over a 6-month follow-up, all dogs were clinically normal when using conventional immunosuppressive therapy. Human IVIG was administered 3 days after initiation of immunosuppressive therapy in 4 dogs, and, after 2 days, in 1 dog. In all dogs, the mean platelet counts pre- and 24 hours post-hIVIG infusion (0.28-0.76 g/kg) were 2,500/pL and 50,600/microL (62,750/microL for the 4 responders), respectively. One dog failed to respond as promptly to hIVIG (0.34 g/kg), and the platelet count increased to 66,000/microL after 9 days of immunosuppressive therapy. The mean duration of hospitalization post-hIVIG in all 5 dogs was 1.8 days (12 hours for responders), and the mean total length of hospitalization was 4.6 days (3.5 days for responders). Active hemorrhage resolved and no packed red blood cell transfusions were required after hIVIG infusion for responders. CONCLUSIONS AND CLINICAL IMPORTANCE: Human IVIG was well tolerated and appeared to be associated with rapid platelet count recovery and amelioration of clinical signs in most dogs with IMT.     

Rescue therapy with doxorubicin-based chemotherapy for relapsing or refractory feline lymphoma: a retrospective study of 23 cases

This study examined the efficacy of doxorubicin-based chemotherapy used for rescue therapy in refractory feline lymphoma. Records of 23 cats with lymphoma treated with chemotherapy who received doxorubicin for the first time in a rescue setting were reviewed. Seventeen (74%) of the 23 cats had only one treatment of doxorubicin. Five (22%) of the 23 cats had a positive response to doxorubicin and were given additional doses. The response to therapy in 4/5 of these responders could be assessed objectively, of which, two cats (9%) achieved partial remission (PR) and two cats (9%) achieved complete remission (CR). The two cats that achieved CR had differing response durations (6 weeks and greater than 47 months). Three of these five (60%) responders had also received concurrent other chemotherapy in addition to doxorubicin. Cell type and the use of concurrent chemotherapy were significant predictors of response. Cats with small-medium cell lymphomas (P=0.001) and cats that received concurrent chemotherapy with doxorubicin rescue (P=0.007) were more likely to respond favorably. This study suggests that doxorubicin-based chemotherapy is not an effective rescue protocol for feline lymphoma.     

Tolerability of Gemcitabine and Carboplatin Doublet Therapy in Cats with Carcinomas

Background: This study was performed to determine the toxicity of gemcitabine-carboplatin doublet therapy in cats with carcinomas.
Hypothesis: Gemcitabine and carboplatin are safe in tumor-bearing cats.
Animals: Twenty cats with spontaneously occurring carcinomas.
Methods: A cohort of 6 cats received gemcitabine (2 mg/kg IV) on days 1, 8, and 15 and carboplatin (10 mg/kg IV) immediately after gemcitabine on day 1 of a 21-day cycle. A 2nd cohort of 14 cats received carboplatin 4 hours after gemcitabine on day 1 and gemcitabine on day 8 but not day 15. The cycles were repeated every 21 days.
Results: Cats in the 1st cohort received a median of 3.75 cycles per animal (range, 1–6). Two cats (33.3%) developed grade 3 or 4 neutropenia, 1 (16.7%) grade 4 thrombocytopenia, and 1 (16.7%) grade 3 gastrointestinal toxicity. Gemcitabine dose reductions and treatment delays occurred in 1 and 4 cats, respectively. Cats in the 2nd cohort received a median of 2 cycles per animal (range, 0.5–10). Two cats (14.3%) had grade 3 or 4 neutropenia and 1 (7.1%) had grade 3 and 4 gastrointestinal toxicity. One cat required gemcitabine dose reduction and 6 had treatment delays. In the 2nd cohort, of 11 cats with measurable tumors, there was 1 complete response (pancreatic carcinoma) and 1 partial response (squamous cell carcinoma, receiving concurrent nonsteroidal anti-inflammatory drugs).
Conclusions and Clinical Importance: Gemcitabine-carboplatin combination appears moderately well tolerated in tumor-bearing cats. Minimal patient benefit suggests that alternative schedules or combinations of gemcitabine with other agents should be explored.     

Platelet size,platelet surface-associated IgG,and reticulated platelets in dogs with immune-mediated thrombocytopenia

Abstract: Immune-mediated thrombocytopenia (IMT) is a disorder in which bound IgG on the surface of platelets results in platelet removal and alterations in mean platelet volume. Using flow cytometry, alterations in platelet size, platelet surface-associated IgG (PSAIgG), and numbers of reticulated platelets were determined in 13 dogs with primary IMT and 4 dogs with secondary IMT induced by experimental infection with Babesia gibsoni . Effects of sample age on platelet parameters also were determined, using samples from 20 dogs with normal platelet counts analyzed within 4 hours and after 24, 48, and 72 hours of storage in EDTA. No significant changes in platelet count, platelet size, or reticulated platelet percentage were observed in samples assayed within 4 and 24 hours of blood collection; whereas PSAIgG values increased 3 to 7 fold in samples stored for 24–72 hours. Using reference values for freshly collected or 24-hour-old samples, 10 of 13 (77%) dogs with primary IMT and all B gibsoni-inf ected dogs had increased PSAIgG levels. In 12 (75%) of the 16 dogs with thrombocytopenia the percentage of reticulated platelets was increased; however, absolute numbers of reticulated platelets were within reference values. Moreover, PSAIgG level and the percentage of reticulated platelets were not always increased concurrently in dogs with primary and secondary IMT. Platelet microparticles were detected in all B gibsoni-infected dogs, 8 of 13 (62%) dogs with primary IMT, and transiently in a dog that responded to immunosuppressive treatment. The results of this study indicate that sample age and time of sampling during disease affect interpretation of platelet parameters in dogs with IMT.     

Development of a sensitive immunoradiometric assay for detection of platelet surface-associated immunoglobulins in thrombocytopenic dogs

OBJECTIVE: To develop a direct assay to measure platelet surface-associated immunoglobulins (PSAIg) in dogs and to determine whether the assay is useful in the diagnosis of immune-mediated thrombocytopenia (IMT). ANIMALS: 20 healthy dogs were used to develop reference intervals, and 23 dogs with IMT and 17 with non-IMT were used to evaluate the clinical use of this assay. PROCEDURE: After optimization of platelet collection and assay conditions, concentrations of PSAIg were measured, using radiolabeled staphylococcal protein A (SpA) and polyclonal antibodies against canine IgG (anti-gamma) and IgM (anti-micro). Concentrations of PSAIg were expressed as the percentage of radiolabeled immunoglobulin detector bound. RESULTS: Cut-off values (mean + 3 SD) were as follows: SpA, 1.1%; anti-gamma, 1.3%; and anti-micro, 3.5%. Values greater than these cut-off values were considered positive. Values determined by use of radiolabeled SpA for all dogs with IMT were greater than the cut-off value; values were considered high positives (> 5 times cut-off value) for 22 of these 23 dogs. Although 9 of 17 dogs with non-IMT also had PSAIg concentrations greater than the cut-off value, values were considered high positives for only 3 of these 9 dogs. CONCLUSIONS AND CLINICAL RELEVANCE: The immunoradiometric assay developed is a reliable and sensitive method to detect PSAIg in dogs. However, to obtain accurate results, optimum temperature, time, and storage conditions must be used. Detection of increased concentrations of PSAIg in dogs presumed to have non-IMT should alert clinicians to reconsider an immune-mediated basis for the thrombocytopenia.     

Erythrocyte dysplasia in peripheral blood smears from 5 thrombocytopenic dogs treated with vincristine sulfate

Secondary dyserythropoiesis has been associated with vincristine administration in dogs. Evaluation of bone marrow aspirates for the presence of morphologic abnormalities in the erythroid lineage aids in the diagnosis. However, morphologic features of circulating erythroid precursors in these cases have not been described previously. The purpose of this report was to describe the cytologic features of dyserythropoiesis in peripheral blood and also bone marrow smears in a case series of dogs with immune‐mediated thrombocytopenia (IMT) treated with vincristine sulfate. Nineteen dogs receiving vincristine for treatment of IMT were identified by retrospectively searching a computerized medical record system. There were 5 dogs that had dysplastic erythroid precursors in peripheral blood smears within 7 days of vincristine treatment. Two of those 5 dogs also had evidence for erythrodysplasia in modified Wright's‐stained bone marrow smears obtained postvincristine administration. Morphologic changes included bizarre or inappropriate mitotic figures, abnormal nuclear configurations (fragmentation, elongation, indentation, and binucleation), atypical nuclear remnants (Howell‐Jolly bodies), or nuclear and cytoplasmic asynchrony within the erythroid precursors. A brief review of the literature with discussion of the etiologies for dyserythropoiesis is provided. The dyserythropoiesis was clinically insignificant in all 5 cases and resolved. However, pathologists and clinicians should be aware of these potential findings to prevent misdiagnosis of other conditions.     

Prevalence of low automated platelet counts in cats: comparison with prevalence of thrombocytopenia based on blood smear estimation

Abstract: True thrombocytopenia is uncommon in cats; however, low platelet counts frequently are found using automated cell counters. Although this discrepancy is a well known problem, the prevalence of low automated platelet counts in feline blood samples has not been documented. We retrospectively compared the prevalence of low automated platelet counts with low blood smear-estimated platelet counts in feline blood samples. Results of blood sample analysis from 359 cats during a 1-year period at the University of Glasgow Veterinary Haematology Laboratory were examined. Smear estimates of platelet number were done in those cases in which records did not indicate adequate platelet numbers. Platelet counts obtained with an impedance counter (Minos Vet, Abx Hematologie) were <200×10⁹ cells/L in 256 samples (71%) and <50×10⁹ cells/L in 43 samples (12%). However, based on estimation of platelet numbers from blood smears, only 11 samples (3.1%) had platelet counts of <200×10⁹ cells/L and 9 samples (2.5%) had counts of <50×10⁹ cells/L. Four cats with thrombocytopenia estimated by blood smear evaluation had clinical signs of a bleeding disorder. Disorders associated with thrombocytopenia included neoplasia, cytotoxic chemotherapy, and infectious diseases. There was no evidence that delay due to mailing of samples was associated with lower automated platelet counts than would have been obtained on the day of sampling. The high prevalence of apparent thrombocytopenia in automated platelet counts was attributed to a combination of platelet aggregation and the impedance method of cell differentiation by size. Vigilance and careful examination of blood smears is required to identify the few cats with true thrombocytopenia.     

Application of therapeutic plasma exchange in dogs with immune-mediated thrombocytopenia

Therapeutic plasma exchange (TPE) is an emerging treatment for dogs with immune-mediated diseases, but reports for treatment of immune-mediated thrombocytopenia (IMT) are lacking. These case reports illustrate the application of centrifugal TPE in 4 dogs with IMT. All dogs presented with severe hemorrhage requiring ≥1 blood transfusions, were unresponsive to conventional treatment or both. Dogs were treated with 3 sequential centrifugal TPE sessions, totaling 4.0 to 4.9 total plasma volumes exchanged per dog. In 3 dogs, TPE was associated with improvement in clinical manifestations of bleeding and platelet count in combination with immunosuppressive drugs. One dog was euthanized after 3 treatments because of persistent severe thrombocytopenia and hemorrhage. Preliminary observations indicate that TPE is safe and may be a useful adjunct in the management of IMT that is severe or refractory to traditional treatment.     

Detection of antiplatelet immunoglobulin in thrombocytopenic dogs

Indirect enzyme-linked immunosorbent assays (ELISA) were used to detect platelet-associated immunoglobulin in sera from dogs with immune-mediated thrombocytopenia (IMT) and/or other autoimmune syndromes. One ELISA, utilizing whole platelets as the antigen substrate, readily detected antibody associated with platelets, either as specific, antiplatelet antibody or as immune complexes. This assay apparently lacked specificity because of the position reactions with sera from dogs with miscellaneous autoimmune disorders and no concurrent thrombocytopenia. Although the second ELISA, utilizing immunoaffinity purified platelet antigens was not influenced as much by immune complexes, absorbance values apparently were slightly increased. However, a small number of dogs with non-thrombocytopenic autoimmune disease tested positive. Immunoadsorption and Western immuno-blotting techniques demonstrated a complex pattern of specificities for antiplatelet antibodies. Clinical significance of these findings is discussed.     

A retrospective study of (90)Strontium plesiotherapy for feline squamous cell carcinoma of the nasal planum

The responses of 15 cats with histologically (n=14) or cytologically (n=1) confirmed nasal squamous cell carcinoma treated with (90)Strontium plesiotherapy were reviewed retrospectively. Cats were treated such that a total dose of 50Gy was delivered at a depth of 2mm, administered in five fractions over a 10-day period. Of the cats, 11 were stage T(2), three were T(is) and one had only a cytological diagnosis precluding staging. Eleven of the cats achieved complete response (no visible lesion after 6-8 weeks) following the first cycle of therapy, and two cats with partial response achieved complete response with a second cycle of therapy. The remaining two cats achieved partial response following therapy, but further intervention was declined. Euthanasia was performed in these two cats because of progressive disease after 81 and 142 days. Of the 85% of cats that achieved a complete response, there was no recurrence of disease during a follow-up period of 134-2,043 days (median 652 days). In addition to prolonged disease-free survivals, (90)Strontium therapy produced excellent cosmetic results from the owners' perspective. These results demonstrate that superficial squamous cell carcinoma of the feline nasal planum responds excellently to (90)Strontium plesiotherapy, and this form of therapy may offer advantages over other alternatives currently available.