An 8‐year‐old, female, spayed, domestic longhair cat presented with progressive pelvic limb weakness, lethargy and weight loss. Physical examination identified bilateral pelvic limb proprioceptive ataxia, tachypnoea and a subcutaneous nodular lesion on the left flank. Investigations documented a diffuse broncho‐interstitial and nodular pulmonary pattern, pyogranulomatous inflammation in the spleen and an intradural‐extramedullary spinal lesion at the level of L3. Mycobacterium microti was confirmed based on demonstration of organisms on histopathology of the subcutaneous nodule using Ziehl–Neelsen stain together with positive polymerase chain reaction and interferon‐gamma release assay results. Therapy with rifampicin, azithromycin and pradofloxacin was administered for 7 months. Serial monitoring, including repeated magnetic resonance imaging, demonstrated resolution of the clinical signs, pulmonary, subcutaneous and spinal lesions.

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Background: Thrombocytopenia is a common laboratory abnormality in dogs, and numerous diseases have been associated with its development. Estimates for the sensitivity and specificity of the degree of reduction of platelet concentration for the diagnosis of primary immune-mediated thrombocytopenia (pITP) have not been reported. Objectives:To report the prevalence of different causes of thrombocytopenia in dogs in the United Kingdom and to investigate the utility of platelet concentration to differentiate causes of thrombocytopenia.Methods: Medical records of 762 dogs with thrombocytopenia presented to seven referral hospitals from January 2017 to December 2018 were retrospectively reviewed. Cases were assigned into the following categories: pITP, infectious diseases, neoplasia, inflammatory/other immune-mediated disorders and miscellaneous causes.The prevalence of the different categories was estimated, and platelet concentrations were compared. Receiver-operating characteristic (ROC) curves were used to investigate the utility of platelet concentration to differentiate between causes of thrombocytopenia. Results:The most common disease category associated with thrombocytopenia was neoplasia (27.3%), followed by miscellaneous causes (26.9%), pITP (18.8%), inflammatory/immune-mediated disorders (14.4%) and infectious diseases (12.6%). Dogs with pITP had significantly lower platelet concentrations (median 8 × 10 9 /L, range: 0-70 × 10 9 /L) than dogs in the other four categories. Platelet concentration was useful for distinguishing pITP from other causes of thrombocytopenia (area under ROC curve = 0.89, 95% confidence interval 0.87, 0.92), with a platelet concentration ≤12 × 10 9 /L being 60% sensitive and 90% specific.