Fine‐Needle Aspirate Cytology of Feline Pulmonary Langerhans Cell Histiocytosis in Two Cats

Feline pulmonary Langerhans cell histiocytosis (FPLCH) is a rare histiocytic disorder in cats, usually diagnosed post-mortem following natural death or euthanasia for severe respiratory distress. Antemortem diagnosis has been reported only once, achieved by cytologic examination of bronchoalveolar lavage fluid combined with immunocytochemistry, whereas fine-needle aspiration (FNA) of lung nodules was previously reported as non-diagnostic. Here we describe two cases of FPLCH in which cytology of ultrasound-guided lung-nodule FNA yielded diagnostic material, including from one cat with an atypical clinical presentation. Whereas case 1 presented with severe respiratory distress, case 2 had no respiratory signs. Both specimens were highly cellular and composed of atypical cells morphologically most consistent with histiocytes showing moderate atypia. A combination of postmortem gross, histopathologic, immunophenotypic, and ultrastructural findings confirmed the cytologic suspicion of FPLCH. To our knowledge, this is the first cytologic description of FPLCH in FNA samples from lung nodules and the first report of a confirmed case without respiratory signs.