Small Number Of Cats Research Articles

Causes and consequences of feline haemothorax: A retrospective case series.

The objective of this study was to describe the causes of haemothorax in cats, patient presentation and outcome. This was a retrospective study based in a university teaching hospital. The electronic case records of cats presenting with a haemothorax between January 2005 and January 2023 were searched. Cases were categorised into 'trauma', 'neoplasia', 'coagulopathy' or 'other'. Signalment, physical examination, clinical pathology findings, concurrent injuries and diagnostic imaging findings were recorded. The median hospitalisation time was calculated, and survival to discharge was noted. Twenty-five cats were eligible for inclusion. Twenty cases of haemothorax were traumatic in origin, two were neoplastic, two were 'other' and one was coagulopathic. Increased respiratory rate (n = 22) and effort (n = 20) were common, and most patients were anaemic at presentation (n = 16). Common concurrent injuries included pulmonary contusions (n = 15) and pneumothorax (n = 11). The median hospitalisation time for the trauma cats was 5 days (range 1‒15). Overall, 83.3% of the cases survived to discharge. The limitations of this study are related to its retrospective nature and the relatively small number of cats in the study population. Haemothorax requiring a thoracocentesis in cats is rare, with trauma being the most likely cause. These patients tend to have concurrent injuries and require ongoing hospitalisation. Owners can be advised that the short-term outcome is generally favourable.

Pegylated-l-asparaginase therapy for feline large cell lymphoma: 82 cases (2017-2020).

The present study aimed to investigate pegylated-l-asparaginase monotherapy for feline large cell lymphoma as a potential alternative to palliative corticosteroids treatment in animals whose owners declined cytotoxic chemotherapy. A retrospective, descriptive case series of cats treated initially with pegylated-l-asparaginase as a sole therapy for feline large cell lymphoma is reported. The treatment protocol consisted of 12 intramuscular injections of pegylated-l-asparaginase with increasing intervals. If cats were unresponsive to pegylated-l-asparaginase monotherapy, a second-line treatment was initiated. Signalment, origin of lymphoma, staging, treatment, possible adverse events and follow-up data were extracted from the medical records. Responses and survival data were analysed. Eighty-two cats with lymphoma of five different anatomic types were included: alimentary, abdominal extra-alimentary, peripheral nodal, nasal/nasopharyngeal and other (mediastinal, renal [solitary] and miscellaneous combined in one group for analytical purposes). The response rate was 74.1% (95% confidence interval = 63.4-83.5) with 38.3% (95% confidence interval = 27.8-48.8) in complete remission. The median disease-free period and calculated overall survival time were 70 days (12-1702+) and 79 days (1-1715+), respectively. The response rate was significantly correlated with the origin of the lymphoma and the combined group had a significantly lower response rate (P = 0.035). Twenty-four cats were also treated with corticosteroids. There was no significant difference in outcomes between the group treated with or without corticosteroids. Adverse events were present in a small number of cats (14/82). The majority of these adverse events were mild to moderate in 5/14 cats; however, the adverse events were severe enough to cause discontinuation of therapy. Based on the response rate and median disease-free period, treatment with pegylated-l-asparaginase is inferior when compared with historical chemotherapy protocols. However, some cats demonstrated an exceptional long disease-free period. Therefore, pegylated-l-asparaginase could be offered as an alternative to corticosteroid therapy alone. Further studies are needed to evaluate the additional benefit over palliative corticosteroid monotherapy.

Clinical differences in enterococcal bacteriuria compared with other bacteriuria in cats.

The clinical differences between Enterococcus species bacteriuria compared with other bacteria has been reported in a small number of cats. The objective of this study was to compare a large number of cats with Enterococcus species bacteriuria to cats with other bacteriuria and determine the clinical differences. It was hypothesized that enterococcal bacteriuria would be associated with subclinical bacteriuria and polymicrobial infections more than other bacteriuria, and that when local or systemic comorbidities were present, enterococcal bacteriuria would be more common. This retrospective case-control study compared case cats with enterococcal bacteriuria to control cats with other bacteriuria. Cats with enterococcal bacteriuria were age, year and weight matched with 1-2 control cats with any other bacteriuria. Lower urinary tract clinical signs were statistically significantly more common in controls (n = 38/77 [49%]) compared with Enterococcus cases (n = 12/47 [25%]; P = 0.01). Specifically, control cats (n = 20/77 [26%]) were statistically significantly more likely to have gross hematuria compared with Enterococcus case cats (n = 3/47 [6%]; P = 0.01). Enterococcus cases were statistically significantly more likely to have a polymicrobial infection compared with controls (odds ratio 5.84, 95% confidence interval 1.33-34.70; P = 0.01). Enterococcus species are associated with subclinical bacteriuria and polymicrobial urinary tract infections in cats vs other bacteriuria.

Should we be screening cats for cardiomyopathy? If so, how?

Occult feline hypertrophic cardiomyopathy (HCM) can result in unexpected sudden death or congestive heart failure (CHF) following routine interventions such as anesthesia, fluid administration, or, potentially, administration of corticosteroids. Consequently, clinicians would like to be able to screen at-risk cats to detect occult HCM and either avoid the risky intervention or attempt to reduce the risk of death or CHF. Currently, the feline N-terminal-proBrain natriuretic peptide test is the only potential screening test for detecting occult HCM. However, some cardiologists have pointed out the poor sensitivity of the test precludes its use as a screening test. This interpretation appears somewhat flawed. Using the current rapid test will allow clinicians to correctly identify half of the cats with moderate-to-severe occult HCM. A small number of cats without HCM will also test positive, necessitating an ultimately needless echocardiographic evaluation to demonstrate their disease-free status. However, the low prevalence of HCM in the general cat population and the apparently much lower rate of adverse events than would be predicted brings into question whether clinicians should bother screening. Therefore, until a more sensitive and accurate screening test becomes available, clinicians will have to decide for themselves whether identifying half of the at-risk cats of sudden death and CHF with this test is better than identifying none of them.

Investigated regional apparent diffusion coefficient values of the morphologically normal feline brain.

Diffusion-weighted imaging (DWI) MRI is increasingly available in veterinary medicine for investigation of the brain. However, apparent diffusion coefficient (ADC) values have only been reported in a small number of cats or in research settings. The aim of this study was to investigate the ADC values of different anatomical regions of the morphologically normal brain in a feline patient population. Additionally, we aimed to assess the possible influence on the ADC values of different patient-related factors, such as sex, body weight, age, imaging of the left and right side of the cerebral hemispheres and white vs grey matter regions. This retrospective study included cats undergoing an MRI (3T) examination with DWI sequences of the head at the Vetsuisse Faculty of the University Zurich between 2015 and 2021. Only cats with morphologically normal brains were included. On the ADC maps, 10 regions of interest (ROIs) were manually drawn on the following anatomical regions: caudate nucleus; internal capsule (two locations); piriform lobe; thalamus; hippocampus; cortex cerebri (two locations); cerebellar hemisphere; and one ROI in the centre of the cerebellar vermis. Except for the ROI at the cerebellar vermis, each ROI was drawn in the left and right hemisphere. The ADC values were calculated by the software and recorded. A total of 129 cats were included in this study. The ADC varied in the different ROIs, with the highest mean ADC value in the hippocampus and the lowest in the cerebellar hemisphere. ADC was significantly lower in the white cerebral matter compared with the grey matter. ADC values were not influenced by age, with the exception of the hippocampus and the cingulate gyrus. ADC values of different anatomical regions of the morphologically normal feline brain in a patient population of 129 cats in a clinical setting are reported for the first time.

Influence of exposure to microbial ligands, immunosuppressive drugs and chronic kidney disease on endogenous immunomodulatory gene expression in feline adipose-derived mesenchymal stem cells.

Feline autologous mesenchymal stem cells (MSCs) show promise for immunomodulatory activity, but the functional impact of chronic kidney disease (CKD), concurrent immunosuppressive drug administration or infection is unknown. The study objectives compare endogenous cytokine gene expression (interleukin [IL]-6, IL-10, IL-12p40, IL-18 and transforming growth factor beta [TGF-β]) in adipose-derived MSCs (aMSCs) from cats with and without CKD, following in vitro exposure to microbial ligands and treatment with common immunosuppressive drugs. Previously obtained aMSCs, phenotype CD44+, CD90+, CD105+ and MHCII-, from cats with (n = 6) and without (n = 6) CKD were compared via real-time PCR (RT-PCR) for immunomodulatory gene expression. aMSCs were exposed in vitro to lipopolysaccharide (LPS), peptidoglycan or polyinosinic:polycytidylic acid (Poly I:C), simulating bacterial or viral exposure, respectively. aMSCs were also exposed to ciclosporin, dexamethasone or methotrexate. Gene expression was measured using RT-PCR, and Cq was utilized after each run to calculate the delta cycle threshold. aMSCs isolated from healthy and CKD cats showed no significant differences in gene expression in the five measured cytokines. No significant changes in measured gene expression after drug treatment or microbial ligand stimulation were observed between normal or CKD affected cats. Proinflammatory genes (IL-6, IL-12p40 and IL-18) showed altered expression in aMSCs from both groups when compared with the same cells in standard culture after exposure to methotrexate. Poly I:C altered IL-6 and TGF-β gene expression in aMSCs from both healthy and CKD cats when compared with the same cells in standard culture. The five genes tested showed no statistical differences between aMSCs from healthy or CKD cats. There was altered cytokine gene expression between the control and treatment groups of both healthy and CKD cats suggesting feline aMSCs have altered function with immunosuppressive treatment or microbial ligand exposure. Although the current clinical relevance of this pilot study comparing brief exposure to select agents in vitro in aMSCs from a small number of cats is unknown, the study highlights a need for continued investigation into the effects of disease and concurrent therapies on use of cell-based therapies in feline patients.

Management of severe stifle trauma: 2. Periarticular fractures.

Periarticular stifle fractures are uncommon but challenging injuries to treat. There may be concurrent damage to the ligaments and stabilising structures of the stifle joint itself, which should also be evaluated (see Part 1 of this article series). Improved knowledge of the fixation options and biomechanical challenges of these injuries will aid clinical decision-making and effective repair. Due to their nature, periarticular fractures may have small juxta-articular fragments, which require additional thought to address during stabilisation. In juvenile animals, these fractures typically involve the physis and often can be managed with cross pin fixation. In adult cats, locking fixation, specialised plates or external skeletal fixators can be utilised to address the juxta-articular fragments. Readers should also be aware of patellar fracture and dental anomaly syndrome (PADS), where cats develop insufficiency fractures affecting the patella and proximal tibia. A careful oral examination should be performed in affected patients, as these cats may have persistent deciduous teeth. Close attention should be paid to preoperative radiographs for evidence of chronicity of the injury including sclerosis of the patella, remodelling and blunting of the fracture lines. The aims of the article are to review the current literature surrounding periarticular fractures of the stifle joint and to summarise the diagnosis, treatment, outcome and complications of each fracture type. As well as discussing general fracture fixation and biomechanical principles applicable to both dogs and cats, information is provided on specific issues facing cats, such as PADS. Published data is limited, with reports including only a small number of cats. The information and recommendations in this article have therefore been drawn from a combination of the available literature and the authors' clinical experience.

Management of severe stifle trauma: 1. Stifle luxation.

Traumatic stifle joint luxation is an uncommon but severe injury. There is usually rupture of several stabilising structures of the joint including the cruciate ligaments, collateral ligaments, joint capsule and menisci. Successful management of this condition requires good anatomical knowledge and repair or replacement of all damaged structures to achieve adequate joint reduction and stability. Better understanding of the treatment options available will aid clinical decision-making. Due to the significant joint instability associated with these injuries, surgical repair is challenging. The use of a temporary transarticular pin to hold the stifle joint in anatomic reduction greatly aids ligament repair or replacement. Postoperative joint immobilisation has traditionally been recommended to protect the primary repair and aid periarticular fibrosis, but prolonged immobilisation can have deleterious long-term effects on the joint. Thus recommendations for the duration of postoperative immobilisation vary between 2 and 6 weeks. Also, due to their independent, outdoor lifestyle, affected cats may have been involved in a significant trauma with important concurrent injuries that need to be addressed prior to the orthopaedic repair. Published data is limited, with reports including only a small number of cats. The information and recommendations in this article have therefore been drawn from the available literature, the authors' experience and preliminary data from an ongoing multicentre retrospective study (unpublished). The aims of this article are to give the reader as thorough a summary as possible of the diagnosis, treatment, outcome and complications of traumatic stifle luxation.

Patent ductus arteriosus in cats

CONGENITAL heart disease (CHD) in cats is uncommon compared with its acquired counterpart. Reports on the prevalence of feline CHD vary from as little as 0.2 per cent to as...

Developing biorobotics for veterinary research into cat movements

Collaboration between veterinarians and other professionals such as engineers and computer scientists will become important in biorobotics for both scientific achievements and the protection of animal welfare. Particularly, cats have not yet become a significant source of inspiration for new technologies in robotics. This article suggests a novel approach for the investigation of particular aspects of cat morphology, neurophysiology, and behavior aimed at bridging this gap by focusing on the versatile, powerful locomotion abilities of cats and implementing a robotic tool for the measurements of biological parameters of animals and building cat-inspired robotic prototypes. The presented framework suggests the basis for the development of novel hypotheses and models describing biomechanics, locomotion, balancing system, visual perception, as well as learning and adaption of cat motor skills and behavior. In subsequent work, the resulting models will be tested and evaluated in simulated and real experiments and validated with specific experimental data gathered from cats. This methodology has application in several areas including dynamic models and artificial vision systems. From an ethical point of view, this approach is in line with the 3R principles: the detailed and integrated systems will allow us to study a small number of cats (reduction) for the implementation of noninvasive tools such as electromyography and gaze analysis (refinement), which will make the construction of a substitute to experiments on living cats (replacement) easier. For instance, bioinspired prototypes could be used to test how specific visual and physical impairment in cats (up to partial or total blindness, loss of a leg, and so forth) change their walking and jumping abilities. This modus operandi may pave the way for a new generation of research in the veterinary field. Moreover, the measurement tools to be developed will constitute an achievement per se as for the first time visual, muscular, and gait analysis of cats will be integrated, and this will help to improve the rehabilitation procedures for cats and other nonhuman animals.

OTITIS EXTERNA AND OTITIS MEDIA IN CATS IN ASSIUT: A RETROSPECTIVE STUDY OF PRESENTING SIGNS, CAUSES, DIAGNOSIS AND TREATMENT

In this study, records of cases admitted to the Small Animal Clinic (SAC), Veterinary Teaching Hospital (VTH) at Assiut University, between years 2007-2011 for investigation of signs of otitis were reviewed and data analyzed. Points of analysis comprised presenting clinical signs, results of otoscopic examination, identification of cause of otitis and outcome of treatment of each cat. Treatments used for these cases were either ivermectin injection or topical treatment with antimicrobial/anti-inflammatory ear drops as well as a ceruminolytic agent for cleansing the ear to increase effectiveness of medications used. Total number of cases with signs of otitis was 76 cats. Otitis cases comprised 19.8% of the total cases presented at the SAC in the study period. The most common presenting signs were head shaking, itching and ear wax in 67.11% of cases. 21.05% of cases were presented with severe inflammation, pain and alopecia around the ear pinna. A small number of cats were presented with signs of alopecia around the ear pinna and concomitant ring worm (3.95%). The remaining 7.89% were presented with very mild ear scratching in one or two ears. Sex was not a confounding factor as both males and females were equally represented among cases (51% males: 49% females). Turkish Angora and Persian cat breeds were over-represented (39.5% and 35.5% respectively). 68 cats were treated with ivermectin injections (1-4 injections) and ten cats were treated with topical antibacterial and anti-inflammatory. 67.11% of treated cases completely recovered and 32.89% of treated cases were not brought back for follow-up visits and therefore information regarding full recovery was not available. When evaluating a patient with otitis externa, it is important to determine the primary cause as well as the predisposing and perpetuating factors of the otitis so as to manage the otitis properly. The first diagnostic procedure that should be performed on a patient with a complaint of otitis externa is an otoscopic examination.

Double-J ureteral stenting in nine cats with ureteral obstruction

Ureteral stenting is a common practice in human medicine and has recently been reported in dogs and cats to provide urinary diversion for ureteral obstructions caused by ureteroliths, strictures, neoplasia, and in an attempt to prevent postoperative complications following ureteral anastomosis. The aim of this report is to describe a surgical technique of ureteral stenting and the follow-up and complications in nine cats. Number 3 French double-J catheters were used during open surgery for ureterotomy/ureterolith removal in eight cats and for segmental ureterectomy/end-to-end anastomosis in one cat for a localized benign stricture. Neoureterocystostomy was necessary in eight of the cats. Uroperitoneum did not occur. Stents were still in place in 7/9 animals after 357-1,565 days (median 1,277 days). A minor complication (stent migration) occurred in one cat, but stent removal was not required. Major complications were encrustation and persistent stranguria (in one cat each), requiring stent removal at 90 and 123 days, respectively. The first cat had a new stent inserted but was euthanased 3 months later for progressive renal failure. Despite the small number of cats, both the outcome and long-term stent tolerance observed in most cases suggest that ureteral stenting is a safe, adjunctive measure to ureteral surgery, mainly for concomitant ureteral and renal pelvic stones to prevent further obstruction and avoid pyelotomy/nephrotomy. However, smaller stents should be used to decrease the need for ureteral surgery.

Comparing citrated native, kaolin-activated, and tissue factor–activated samples and determining intraindividual variability for feline thromboelastography

Thromboelastography (TEG) is a point-of-care whole blood test of hemostasis. While TEG is becoming more widely used in veterinary medicine, few studies describe the use of TEG in cats. The objectives of the current study were to: 1) document the range of TEG variables produced in healthy cats using 3 sample types (citrated native, kaolin-activated, and tissue factor-activated), and 2) determine if there was a significant difference between 2 separate samples obtained from individual healthy cats on the same day. Jugular venipuncture was performed in 20 cats, and citrated blood collected for TEG. TEG analysis was performed on citrated native, kaolin-activated, and tissue factor-activated blood for each sample. Two hours later, the procedure was repeated from the opposite jugular vein, yielding a total of 120 analyses. Reaction time (R), alpha angle (α), kappa value (κ), and maximum amplitude (MA) were recorded from each tracing. No significant differences were found between TEG tracings from the first and second venipuncture samples. Significant differences were found between sample types for R, α, κ, and MA. Means for citrated native/kaolin-activated/tissue factor-activated methods were R = 4.1/3.7/0.6 min; κ = 2.5/1.8/2.2 min; α = 59.9/65.1/70.4 degrees; MA = 47.4/49.9/44.7 mm. A limitation of this study was the small number of cats used. Thromboelastography analysis may be a suitable method of evaluating hemostasis in cats.

Comparison of direct immunofluorescence, modified acid-fast staining, and enzyme immunoassay techniques for detection of Cryptosporidium spp in naturally exposed kittens

To evaluate a modified Ziehl-Neelsen acid-fast staining technique (mZN), a direct immunofluorescence detection procedure (DIF), and 3 commercial enzyme immunoassays (EIAs) for detection of Cryptosporidium oocysts in fecal specimens from kittens. Prospective study. 416 fecal specimens collected from 104 randomly selected domestic shorthair kittens (8 to 16 weeks of age) that were naturally exposed to Cryptosporidium spp. Fresh fecal specimens were collected once daily for 4 consecutive days and processed immediately. Sensitivities of mZN, DIF, and 3 commercial EIAs (EIA-1, EIA-2, and EIA-3) were estimated and compared. EIA-2 had the highest sensitivity on day 1 (89%), followed by EIA-1 (80%), and mZN (72%). EIA-3 had the lowest sensitivity on day 1 (15%). EIA-2, EIA-1, and mZN had similar sensitivities after 2 consecutive fecal examinations (approx 90%). Determination of specificities was compromised by the small number of cats that had negative results for all tests (n = 3). Results suggest that EIA-2 and EIA-1 had the highest sensitivities when only a single fecal specimen was examined; however, mZN and EIA-1 had similar sensitivities when 2 consecutive fecal specimens were examined. The higher costs of EIA-2 and EIA-1 may be offset by the tests' high sensitivity, simplicity of use, and ease of interpretation and by savings in technician time.

Prevalence of antibodies to Bartonella henselae, B. elizabethae and B. quintana in Swedish domestic cats.

Sera from 292 cats were analyzed by means of indirect immunofluorescence for antibodies to Bartonella henselae, B. quintana and B. elizabethae. The sera were sent to the Swedish National Institute of Veterinary Medicine for health monitoring and were tested retrospectively for antibodies to Bartonella. The most prevalent antibodies (25%) reacted with the B. elizabethae antigen. Cats with such antibodies were older than those without antibodies. The prevalence of antibodies to B. elizabethae was higher in the south of Sweden than in the north, with the highest prevalence (46%) being found in cats living in the Stockholm region. There was no difference in sex distribution. A low prevalence (1%) of antibodies to B. henselae was found and no sera reacted with B. quintana. The high prevalence of antibodies to B. elizabethae is consistent with previous findings in Swedish patients. The small number of cats with B. henselae antibodies observed in this study could be due to the cold climate and the low occurrence of cat fleas in Sweden.

Measurement of serum bile acids concentrations for diagnosis of hepatobiliary disease in cats

Summary Serum bile acid concentrations were measured after food had been withheld for 12 hours (fasting serum bile acid [ fsba] concentration) and 2 hours after a meal (postprandial serum bile acid [ psba] concentration) using a direct enzymatic procedure in 108 cats clinically suspected of having hepatobiliary disease. In all cats, liver tissue was examined histologically to confirm the diagnosis. Twenty-six cats did not have histologic evidence of hepatobiliary disease and served as controls. The remaining 82 cats had hepatobiliary disease including hepatic lipidosis (n = 20), portosystemic vascular anomaly (n = 24), hepatic necrosis (n = 13), hepatic neoplasia (n =8), or cholestatic hepatic disease (n = 17). Sensitivity and specificity of measuring fsba and psba concentrations were calculated for each test alone and when results were interpreted in combination (ie, in series and in parallel), and were compared with sensitivity and specificity of routinely used serum biochemical tests, including measuring serum activities of alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, and γ- glutamyltransferase, and measuring serum concentrations of cholesterol, bun, and total bilirubin. When tests were considered individually, determination of fsba and psba concentrations had higher specificity than did the other tests (using a cutoff of 15 μmol/L for fsba concentration and of 20 μmol/L for psba concentration). Determination of psba concentration had the highest sensitivity of all single tests in cats with hepatic lipidosis, portosystemic vascular anomaly, or cholestasis; determination of alanine aminotransferase activity or psba concentration had the highest sensitivity for cats with hepatic neoplasia; and determination of aspartate aminotransferase activity had the highest sensitivity for cats with hepatic necrosis. For all cats with hepatobiliary disease, determination of psba concentration had the highest sensitivity of any single test. Combination testing using results of measuring total serum bile acid concentrations in conjunction with results of measuring serum enzyme activity or total bilirubin concentration gave the best overall test performance. Results indicate that both the fsba and psba concentration should be determined, but that if paired samples cannot be collected, the psba concentration should be preferentially measured. In a small number of cats (6/108), the fsba concentration exceeded the psba concentration.

Classification of myeloproliferative disorders in cats using criteria proposed by the animal leukaemia study group: A retrospective study of 181 cases (1969–1992)

Bone marrow cytology in Wright or Wright Giemsa stained smears from 181 feline patients were evaluated according to recently published criteria by the animal leukaemia study group for classification of acute] myeloid leukaemas (AML) and myelodysplastic syndrome (MDS). AML was recognised in 107 (59.1%) and MDS in 39 (21.5%) cats. The frequency of acute myeloblastic leukaemia (M1 and M2 combined) was high (30.9%), erythroleukaemia (M6 and M6-Er combined) was relatively less frequent (17.1%), and acute undifferentiated leukaemia (AUL), acute monoblastic leukaemia (M5) and acute myelomonocytic leukaemia (M4) were less common, each with an incidence of less than 5.0%. Most of the M1 cats had greater than 70.0% blast cells in bone marrow compared to only a few of the M2 cats. Some blast cells in occasional AUL cats showed cytoplasmic differentiation to either erythroid or myeloid lineage or rarely to both. Type I (classical) myeloblasts predominated in all Ml cats, but occasional type II myeloblasts were seen in some cats and a few cats had some type III myeloblasts. Rubriblasts were prominent in most of the M6-Er cats. Dysplastic changes were more common in M2 than in M1 cats and included primarily dysgranulopoiesis (giant metamyelocytes and bands) and dyserythropoiesis (megaloblastic rubriblasts and rubricytes) and rarely dysmegakaryocytopoiesis (abnormal nuclear morphology). Dysplastic changes involving primarily the erythroid series were seen in M6 and M6-Er cats. Dysmyelopoiesis, in the form of occasional giant metamyelocytes and band neutrophils, was also seen in most cats considered to have myeloid hyperplasia unassociated with leukaemia or MDS. Two M2 and two MDS cats had high (>10.0%) eosinophils in bone marrow and were designated M2-Eos and MDS-Eos, respectively. Cytochemical staining was performed on bone marrow smears from 65 cases to demonstrate myeloid markers such as alkaline phosphatase (ALP), peroxidase (PO), chloroacetate esterase (CAE), and Sudan black B (SBB) and monocytic markers such as α-naphthyl acetate esterase (NAE) and a-naphthyl butyrate esterase (NBE). NAE and NBE staining reactions were usually complementary. Cytochemical heterogeneity and lineage infidelity were observed in some AML subtypes. Blast cells were positive for myeloid markers in many but not all cases of Ml and M2. Similarly monocytic markers were evident in some but not all cases of M4 and M5. Monocytic markers were also evident in blast cells of one M1 and three M2 cases, myeloid markers were present in two cases of M4, and both myeloid and monocytic markers were demonstrated in one case of AUL. Blast cells were negative for both myeloid and monocytic markers in most cases of AUL and M6. ALP-positive cells were increased distinctly (>10.0%) only in a small number of cats (15.4%) which included cases of M1, M2, M4. M6 and MDS. Prominent haematological abnormalities in most of the AML and MDS cases included moderate to severe thrombocytopenia, normocytic normochromic non-regenerative anaemia, normoblastaemia, leukocytosis accompanied by a left shift, and a variable number of circulating blast cells. Circulating blast cell counts of ⩾30.0% were seen in only 15.3% cats. Mean leukocyte counts were over 100 000/µl in most of the M5 and M4 cats and in an occasional M1 cat, whereas AUL cats generally had leukocyte counts within the normal range. Leukopenia was evident in slightly over half of the MDS-Er cats, in nearly a third of the M2 cats, and in a small number of cats in other categories. Monocytosis was most pronounced in M5 cats and prominent in M4 cats. Other abnormalities seen in a small number of cats included hyperproteinaernia or hypoproteinaemia, hyperfibrinogenaemia, elevated icterus index, and thrombocytosis.