What is a systematic diagnostic algorithm for the coughing cat including differentiating asthma from pleural effusion?

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The provided sources do not contain a systematic diagnostic algorithm for the coughing cat, specific diagnostic cutoffs for feline asthma, or quantitative criteria distinguishing asthma from pleural effusion. What the sources do address is the radiographic and clinical challenge of discriminating cranial mediastinal masses from pleural effusion in cats, and the clinical features associated with different causes of pleural effusion. Radiographic discrimination of cranial mediastinal mass versus pleural effusion is the central diagnostic challenge when a cat presents with cranioventral opacity on right lateral thoracic radiographs. Pleural effusion accumulates cranioventrally on lateral views and cannot be distinguished from soft tissue radiographically, and when both a mass and effusion are present simultaneously, the effusion obscures the mass.1 Dorsal tracheal deviation occurs in cats with pleural effusion alone — not only with cranial mediastinal masses — making tracheal position an unreliable sole discriminator.1 The most common mediastinal malignancies in cats are lymphoma and thymoma, with other causes including ectopic thyroid tissue, mediastinal cysts, granulomas, and rare neoplasms.1 Common causes of pleural effusion in cats include congestive heart failure (CHF), neoplasia, pyothorax, and feline infectious peritonitis (FIP).1 Hypothermia at presentation supports CHF as the cause of pleural effusion, though the absolute temperature difference between CHF and non-CHF cats is too small to be used as a standalone discriminator.2 A high proportion of cats with pericardial effusion have concurrent CHF, though FIP has also been reported as a leading cause of pericardial effusion.2 Ultrasound-guided cytology is the definitive next step when a mediastinal mass is suspected. Percutaneous fine-needle aspiration of a cranial mediastinal mass can yield cytomorphologic features consistent with mediastinal lymphoma, as demonstrated via intercostal approach.3 Ultrasound ch