(Note: this manuscript will not discuss heart disease as a cause of cough in cats. This topic will be addressed in the cardiology stream.)
Owners may mistake other clinical signs for coughing in cats. Specifically, many owners believe their cat is 'coughing up a hairball'. In fact, a hairball in the stomach may be expelled via the vomiting reflex. This it is not a cough. If one is not sure that the patient is actually coughing at home, ask the owner to videotape the clinical signs to be sure that coughing is actually the clinical sign that the owner is concerned about.
For better or worse, there are only a limited number of tests available in general practice to determine the cause of feline cough. However, there are only a few disorders of the feline respiratory tract that cause significant cough.
Diagnosis
History
The very first question the author asks an owner of a cat with a cough is whether the patient is exposed to environmental irritants. Cigarette, pipe or cigar smokes are the most common culprits. Cold dry air that is generated in homes with a winter season can cause occasional cough, as can smoke from a fireplace. Additionally, dusty cat litter, air fresheners and ozone-generating air purifiers can also cause coughing in feline patients.
The second question is whether the patient is indoors exclusively and whether the patient is exposed (or has been exposed) to other cats. Exposure to viral and bacterial pathogens of the respiratory tract is unlikely in a single indoor cat household.
Physical Examination
Auscultation is not as helpful a diagnostic tool as we would wish, primarily because our patients perform tidal breathing. When our physicians examine us, they ask us to take in deep breaths. This is because most abnormal respiratory sounds are more obvious during exaggerated breathing; tidal breathing causes adventitious sounds only when the disease state is advanced. However, the presence of crackles or wheeze always represents significant pathology within the bronchopulmonary tree.
If the patient has exaggerated respiratory motions during inspiration the disorder is likely to be confined to the upper airway or pleural space. Conversely, if expiration is exaggerated the clinical signs are more likely to be the result of pathology within the lower airways.
Fever is usually the result of upper airway viral infections or bacterial (less commonly fungal) pneumonia. However, patients with fever often appear systemically ill, and an acutely 'sick' cat with fever is not easily distinguished from a 'sick' cat with the disease that is causing the fever.
Chest Radiographs
The interpretation of thoracic radiographs in cats is problematic for a few reasons. First, chest radiographs may appear normal, and this is somewhat common in cats with bronchial disease. Second, cat mucus is particularly tenacious and can cause random mucoid plugging of small airways. This can appear as multiple, patchy, ill defined, fluffy infiltrates that can mimic changes associated with neoplasia, fungal infection and atypical heart failure.
Bronchial disease may result in thickened bronchial walls. These walls cause the 'doughnut' appearance when seen end on, and the 'tram line' appearance when viewed laterally.
Interstitial disease often causes a bronchointerstitial pattern that is strikingly similar to the changes associated with bronchitis or asthma.
Lung disorders will cause some combination of an interstitial and/or alveolar pattern. Pneumonia may cause clinical signs 1-3 days prior to the development of alveolar consolidation on plain radiographs. Conversely, the patient may get clinically better days before the radiographs show improvement.
Neoplastic lung disorders can progress slowly, over 6-18 months. Lung infiltrates seen on radiographs that do not progress over time are less likely to be neoplastic. Conversely, progressive increases in size over months suggest a neoplastic process in older patients.
Lobar infiltrates with punctate lucencies may be the result of lobar abscesses. Antibiotic treatment leading to only partial resolution of these infiltrates may occur.
Pulse Oximetry
The pulse oximeter can be used in patients who are awake. The author usually uses a 'rectal probe' to determine oxygen haemoglobin saturation in awake cats. Patients with respiratory disease may need supplemental oxygen. The pulse oximeter can be used to determine whether an individual patient requires oxygen, and can also be used to determine when oxygen is no longer required. In general, a pulse oximetry reading of 95% and above reflects sufficient oxygenation and supplemental oxygen is not clearly required. A reading of 90% or less represents a PaO2 of 60 mmHg or less and is an indication for immediate oxygen supplementation.
Bronchoscopy and Bronchoalveolar Lavage
These are most helpful in determining lobar infiltrates that are neoplastic in origin. Culture of the bronchoalveolar lavage (BAL) fluid is of course helpful in determining the presence of lung infection and the proper choice of antibiotic. Cytology of BAL fluid is otherwise not helpful in distinguishing one non-neoplastic cause of cough from another.
Therapy
Treatment is clearly based on the disease that is present. A few comments are generally true:
Standard doses of many antibiotics are not sufficient to achieve therapeutic levels in bronchial tissue. There is a 'blood-bronchus' barrier that limits penetration of many of these antibiotics, due to lipid solubility, pH etc. In general, penicillins and cephalosporins do not penetrate well.
It is well documented that cats are relatively resistant to side effects of corticosteroid administration compared with dogs. Having said that, we must be equally concerned to use only the proper dose of corticosteroid and for the proper length of time. Specifically, injectable and repository steroids are not indicated for cats with non-infectious causes of cough unless oral and inhaled forms are not available or possible.
Antihistamines are less helpful in treating cats with 'allergies' compared with dogs. This is because the primary preformed mediator in mast cells of cats is serotonin, instead of histamine.
If cough is due to primary nasal disease with postnasal drip, decongestant nasal drops may be very helpful to resolve the cough.