Performance of lymph node cytopathology in diagnosis and characterization of lymphoma in dogs

Abstract

Background: Cytopathology is a minimally invasive and convenient diagnostic procedure, often used as a substitute for histopathology to diagnose and characterize lymphoma in dogs.

Objectives: Assess the diagnostic performance of cytopathology in diagnosing lymphoma and its histopathological subtypes in dogs.

Animals: One-hundred and sixty-one lymph node samples from 139 dogs with enlarged peripheral lymph nodes.

Methods: Based only on cytopathology, 6 examiners independently provided the following interpretations on each sample: (a) lymphoma vs nonlymphoma; (b) grade and phenotype; and (c) World Health Organization (WHO) histopathological subtype. Histopathology and immunohistochemistry (IHC) findings were used as reference standards to evaluate diagnostic performance of cytopathology. Clinical, clinicopathologic, and imaging data also were considered in the definitive diagnosis.

Results: Classification accuracy for lymphoma consistently was >80% for all examiners, whereas it was >60% for low grade T-cell lymphomas, >30% for high grade B-cell lymphomas, >20% for high grade T-cell lymphomas, and <40% for low grade B-cell lymphomas. Interobserver agreement evaluated by kappa scores was 0.55 and 0.32 for identification of lymphoma cases, and of grade plus immunophenotype, respectively.

Conclusions and clinical importance: Cytopathology may result in accurate diagnosis of lymphoma, but accuracy decreases when further characterization is needed. Cytopathology represents a fundamental aid in identifying lymphoma and can be used as a screening test to predict grade and phenotype. However, these results must be confirmed using other ancillary techniques, including flow cytometry, histopathology, and immunohistochemistry (IHC).

Keywords: accuracy; grade; morphology; phenotype.

FIGURE 1

Flowchart depicting the structure of the online questionnaire fulfilled by 6 examiners examining 161 canine lymph node aspirate cytological preparations

FIGURE 2

WHO histopathological classification of 161 canine nodal samples. B‐LBL, B‐cell lymphoblastic lymphoma; BLL, Burkitt‐like lymphoma; B‐SLL, B‐cell small lymphocytic lymphoma; DLBCL, diffuse large B‐cell lymphoma; FL, follicular lymphoma; LGL, large granular lymphocyte lymphoma; MZL, marginal zone lymphoma; nL, negative for lymphoma; PTCL, peripheral T‐cell lymphoma; T‐LBL, T‐cell lymphoblastic lymphoma; T‐SLL, T‐cell small lymphocytic lymphoma; TZL, T‐zone lymphoma

FIGURE 3

Expected predictive values of cytopathological classification of canine nodal lymphoma, based on the sensitivity and specificity values reported in Table 3. Orange lines: positive predictive value (PPV). Blue lines: negative predictive value (NPV). Gray‐shaded areas represent the prevalence range reported in the literature (see methods section for details). (A) PPV and NPV for the identification of high grade B‐cell lymphoma. (B) PPV and NPV for the identification of low grade B‐cell lymphoma. (C) PPV and NPV for the identification of high grade T‐cell lymphoma. (D) PPV and NPV for the identification of low grade T‐cell lymphoma. PV, predictive value