Thoracic disease in the cat can present as one of a multitude of disorders. Many of the problems are treatable pending a definitive diagnosis while others are classified as non-treatable. It is important for the practitioner to accurately identify the exact disease process in order to implement what might end up to be life saving treatment. On the other hand, the early recognition of a non-treatable disease in a dyspneic patient can avoid protracted suffering to the cat and excess expense to the client.
Dyspnea and tachypnea are the most characteristic signs of feline pulmonary and pleural diseases. Although coughing is a sign frequently associated with tracheal and bronchial disorders, the clinician should be aware that most feline pulmonary and pleural disorders are not associated with coughing. Because the dyspneic cat is often in critical status, the primary clinical objective is to expediently diagnose the cause and simultaneously provide supportive treatment.
The etiologies of respiratory embarrassment can involve lesions anywhere along the respiratory tract, the pleural space, or the heart. Therefore it behooves the clinician to obtain a complete history and perform a detailed physical examination in order to accurately localize the primary lesion. Emergency situations might initially require an abbreviated history and physical followed by a more detailed study following the patient's stabilization.
The diagnosis of most thoracic diseases in the cat usually requires the use of diagnostic aids. Depending on the problem at hand, such tests might include: hemograms, serum biochemistry determinations, cytology and culture of respiratory secretions, serology, electrocardiography, tissue biopsy, and thoracic radiography. To avoid compounding the stress to the dyspneic cat, certain diagnostic procedures might have to await the clinical response to symptomatic emergency therapy in order to avoid iatrogenic complications.
The criteria for classifying thoracic disease will vary amongst the internist, radiologist and pathologist. Since chest radiography is one of the most informative diagnostic tools, this manuscript will discuss the feline pulmonary and pleural diseases on the basis of radiographic abnormalities. Because of space constraints, only the most common abnormalities will be discussed.
I. ALVEOLAR ABNORMALITIES
Radiographically alveolar signs consist of fluffy, ill-defined, cotton candy type of infiltrates associated with the presence of air bronchograms and/or air alveolargrams. This pattern may be localized or disseminated depending on the etiology and the duration of disease. The most common causes of an alveolar pattern abnormality in the cat include pulmonary edema of cardiogenic origin, non-cardiogenic pulmonary edema associated with electrical shock and toxic irritants, pneumonia (bacterial, hypersensitivity, mycotic, protozoan), and pulmonary hemorrhage (coagulopathies, trauma), and atelectasis. These disorders are outlined in Table 1.
Table 1. Characteristics of Some Disorders Causing Pulmonary Alveolar Infiltrates in the Cat
|
Disease |
Predisposing or Direct Cause |
Other Diagnostic Findings |
Treatment Principles |
Prognosis |
|
Bacterial pneumonia |
1. Viral respiratory infection
2. Aspiration
3. Primary/idiopathic |
- Fever
- Leukocytosis
- Radiographic lobar involvement; ventral common
- Tracheal wash cytology: WBC's, bacteria |
1. Maintain hydration with parenteral fluids
2. Provide O2
3. Antibiotics
4. Bronchodilating drugs |
Fair to guarded |
|
Chemical pneumonitis |
1. Smoke inhalation
2. Aspiration of oral or gastric secretions |
- History & physical findings obvious with smoke inhalation
- Aspiration commonly occurs with altered consciousness or iatrogenic
- Bacterial pneumonia commonly
complicates |
1. Assure patent upper airway
2. Broad spectrum antibiotics
3. Bronchodilating drugs |
Fair to guarded |
|
Cardiogenic pulmonary edema |
1. Cardiomyopathy
2. Hyperthyroid-induced myocardial hypertrophy
3. Congenital
4. Acquired valvular disorders |
- Characteristic auscultable findings: murmurs, gallop rhythm, arrhythmias
- Radiographic cardiomegaly with pleural effusion or alveolar infiltrate
- EKG & echocardiographic changes |
1. Provide O2
2. Furosemide
3. Specific cardiac drugs depending on exact pathology |
Guarded to grave |
|
Noncardiogenic (neurogenic) pulmonary edema |
1. Electrocution
2. Post seizure |
- Electrocution: acute onset, oral burn, dorsocaudal radiographic pulmonary alveolar infiltrate
- Post seizure |
1. Furosemide
2. Provide O2 cage
3. Avoid dehydration |
Guarded to good |
II. INTERSTITIAL PULMONARY DISEASES
Interstitial diseases primarily involve the supportive tissues of the lung leaving the air spaces grossly uninvolved. Sometimes the underlying diseases allow the accumulation of fluid and/or cells to eventually reduce the air content of the lung tissue by reducing the size of the alveoli or by compressing the air spaces. Interstitial patterns are characterized as increases in pulmonary background density associated with changes in the interstitial structures which cannot be individually recognized; or they can appear as more distinct nodular, linear, or reticular type patterns. Air bronchograms are not associated with interstitial diseases except when certain disorders extend beyond the interstitium to also involve the alveoli. Examples and descriptions of feline interstitial diseases are provided in Table 2.
Table 2. Characteristics of Selected Feline Interstitial Lung Diseases
|
Disease |
Cause |
Helpful Ancillary Clinical Findings |
Treatment |
Prognosis |
|
Interstitial edema |
Cardiomyopathy, & other causes of congestive heart failure
(2) Noncardiogenic
1. hypoalbuminemia
2. IV fluid overload
3. electrocution
4. viral infections
5. toxic inhalants |
Gallop rhythm, echo- & electrocardiographic abnormalities, cardiomegaly
History of exposure to toxic inhalants, viral infections, iatrogenic fluid overload, electric cords |
(1) Diuretics, O2, specific cardiac drugs such as digoxin or propranolol depending on type of cardiac pathology
(2) Diuretics, O2, removal of insulting agent, theophylline |
(1) Guarded to grave
(2) Good to poor depending on associated cause |
|
Interstitial pneumonia |
Viral respiratory disease |
Fever, nasal discharge, sneezing, conjunctivitis, oral ulcerations, history of exposure to infected cats, viral isolation |
Supportive: maintain hydration & nutrition, antibiotics for 20 bacterial complications |
Good to fair |
|
Granulomatous disease |
Systemic mycoses, toxoplasmosis, irritating inhalants, immune-mediated disease |
Knowledge of geographic origin where mycotic disease prevails; dietary & environmental history; presence of other coexisting organ abnormalities; serology; tissue biopsy |
Toxoplasmosis-pyrimethamine & sulfadiazine; clindamycin
Histoplasmosis & blastomycosis - Amphotericin B
Immune mediated disease--immunosuppressants |
Fair to grave |
|
Pulmonary fibrosis |
Healing phase of several disease processes; sometimes idiopathic; old age change |
History of prior pulmonary inflammatory disease; normal hematologic & cytologic test results; sometimes history reveals chronic coughing; absence of other physical abnormalities |
Bronchodilating drugs such as theophylline or aminophylline; occasional short-term use of glucocorticoids |
Fair to poor |
|
Metastatic lung neoplasia |
Extrapulmonary source of malignant neoplasia, i.e.. mammary adenocarcinoma |
Coughing is rare; location of primary source of neoplasia via physical exam, radiography, or surgery; tissue biopsy with histopathologic confirmation; needle aspiration cytology |
Chemotherapy; surgical removal of primary tumor if indicated |
Usually grave |
|
Primary lung neoplasia |
Example; bronchogenic carcinoma |
Physical exam might reveal muffled chest sounds on the involved side; radiography strongly suspicious; neoplastic cells on needle aspirate or surgical biopsy specimens; cough is rare unless there is bronchial impingement |
Chemotherapy, surgical removal |
Usually grave |
|
Lung worms |
Aleurostrongylosis |
Mixed pattern on radiographs; findings of larval forms on fresh fecal smears & Behrman technique; coughing a common associated finding; eosinophilia on hemogram |
(a) Levamizole - 20 to 30 mg/kg once every other day for five treatments
(b) Fenbendazole 50 mg/kg/day x 3 d |
Good |
|
Lung fluke |
Paragonimus kellicotti |
Radiographs: solid or cavitated, circumscribed densities usually in caudal lobes; coughing common, fluke eggs on fecal, eosinophilia |
(a) Albendazole - 50 mg/kg/day minimum of 14 days
(b) Fenbendazole 50 mg/kg/day x 10 d
(c) Praziquantel 25 mg/kg Q 8 h x 2 d |
Good to fair |
|
Heartworms |
Dirofilaria immitis |
Diffuse interstitial infiltrate; pulmonary artery enlargement; +right heart enlargement; eosinophilia |
Author does not recommend thiacetarsamide treatment; treat
symptomatically with glucocorticoids & for heart failure (if present) |
Guarded |
III. BRONCHIAL DISEASE
In the cat, bronchial disease is well typified in the "feline bronchial asthma syndrome." Thoracic radiography reveals characteristic accentuation of the bronchovascular markings. The bronchial wall thickening is caused by bronchial mucosal cell hyperplasia, thickening of the smooth muscular layer, and peribronchiolar cellular infiltrates consisting of eosinophils and mononuclear cells. On the radiograph, the thickened bronchi appear as "doughnuts."
The exact cause of feline bronchial asthma is unknown, although a hypersensitivity is suspected due to the histopathologic changes and the good response to glucocorticoid drugs. The history denotes paroxysms of a dry hacking cough alternating with periods of normalcy. Usually there is no traceable allergen in the history. With time the cough worsens and exercise intolerance occurs. The cat then presents in acute respiratory distress.
The pertinent physical examination findings vary with the stage of disease. The respiratory pattern ranges from normal to overt dyspnea. Lung sounds are normal or harsh. Sometimes moist crackles can be auscultated. A cough may or may not be present at the time of examination.
Characteristic diagnostic findings include radiographically thickened bronchi and occasionally eosinophilia on the hemogram. Transtracheal wash cytology reveals many eosinophils without signs of infection.
Treatment consists of intravenous glucocorticoids and intramuscular aminophylline during times of crises. In extreme states 1/2-3/4 cc of epinephrine (diluted to 1:10,000) can be given IM. In less urgent circumstances, oral prednisolone can be given for a 1-2 week period. Where oral prednisolone cannot be given, the author has found success with the use of Depo-Medrol (UpJohn Company, Kalamazoo, MI) at a dose of 10-20 mg given IM. Repeated treatment depends on the frequency of relapse.
The prognosis is usually excellent, but the owner should be warned of future relapses. Chronic recurring disease will predispose to chronic bronchitis or fibrosis and require the long-term use of bronchodilating drugs.
IV. PLEURAL EFFUSIONS
Pleural effusion denotes a collection of fluid in the pleural space. Grossly the liquid is characterized as blood, chyle, pus or when nondistinctive, as plain effusions. It might be broadly classified as a transudate or an exudate; the former having a lower specific gravity and protein content than the latter.
Pleural effusion is formed under the following general circumstances: (1) an imbalance of the transpleural hydrostatic pressure (congestive heart failure) or protein osmotic forces (hypoalbuminemia), (2) a change in the permeability of the membrane (pleuritis), (3) a decrease in the rate of reabsorption (pleuritis and lymphatic obstruction), or combinations of these mechanisms. The consequences to the patient by the mere presence of the fluid include decreases in lung vital capacity and total lung capacity.
The clinical signs of pleural effusion depend on the underlying etiology. It is important to consider the effusion only as "the tip of the iceberg". It behooves the clinician to determine the underlying cause in order to establish an accurate prognosis and formulate a specific treatment plan. The basic sign in all cats with moderate to large amounts of pleural effusion is dyspnea. Cough is seldom present unless the underlying cause results in bronchial or tracheal compression or irritation.
The classic radiographic features of pleural effusion include: loss of detail of the cardiac outline, incomplete expansion of the lungs, fissure lines, blunting of the caudal lung lobe angles, scalloped lung lobe borders, and sometimes pleural thickening. Other thoracic radiographic abnormalities will depend on the specific cause. When thoracic detail is obscured, it is important to repeat the radiographs following chest drainage to help identify any underlying cause.
There are several etiologies of pleural effusion in the cat. Table 3 provides a clinical description of the more common types.
Table 3. A Clinical Description of the Causes of Pleural Effusion in the Cat
|
Cause |
Associated Physical Findings |
Associated Clinical Findings |
Fluid Type and Characteristics |
Treatment |
Prognosis |
|
Congestive cardiomyopathy |
- Dyspnea
- Muffled chest sounds
- Sometimes heart murmurs
- Cardiac gallop rhythm
- Rarely ascites
- Occasionally aortic thromboembolism |
(1) Characteristic electrocardiographic abnormalities
(2) Oftentimes mild BUN elevations & moderate liver serum enzyme elevations
(3) Radiographically generalized cardiomegaly with pulmonary interstitial or alveolar pattern along with pleural effusion |
(1) Obstructive effusion
(2) Serous, pseudochylous, or serosanguineous
(3) Modified transudate
(4) Cytology: initially mainly RBC's & lymphocytes with smaller numbers of neutrophils, macrophages, & mesothelial cells |
(1) Removal of fluid by thoracentesis
(2) O2
(3) Diuretics
(4) Digoxin
(5) Taurine 500 mg bid |
Guarded to grave |
|
Lymphosarcoma |
- Dyspnea
- Muffled chest sounds (sometimes mainly anteriorly)
- Noncompressible anterior thorax
- Sometimes fever
- Occasionally other organ involvement |
(1) Sometimes anemia
(2) Rarely lymphocytosis with anaplasia
(3) (+) FeLV
(4) Radiographically: anterior mediastinal mass causing tracheal elevation & posterior displacement of the heart
(5) Ocular fundoscopic changes occasionally
(6) Neoplastic lymphocytes on aspirate cytology of the mass
(7) Rarely hypercalcemia |
(1) Obstructive effusion
(2) Serous or serosanguineous
(3) Modified transudate or exudate
(4) Cytology: anaplastic lymphocytes with mixture of RBC, mesothelial cells, macrophages & neutrophils |
(1) Thoracocentesis
(2) Chemotherapy |
Guarded to grave |
|
Pyothorax |
- Dyspnea
- Fever
- Sometimes dehydration
- Muffled chest sounds |
(1) Leukocytosis with left shift
(2) Radiographically: no cardiomegaly or thoracic masses; pleural thickening
(3) Bacterial growth on culture |
(1) Septic inflammatory
(2) Purulent or sanguinopurulent
(3) Pure exudate
(4) Cytology: many neutrophils containing bacteria, free bacteria, toxic neutrophils, mononuclear cells |
(1) Thoracocentesis
(2) Thoracic lavage
(3) Antibiotics |
- Good to poor
- Lung abscess & chronic pleuritis are possible
sequele |
|
Infectious feline peritonitis-"wet-form" |
- Dyspnea
- Fever
- Muffled chest sounds
- Occasionally corneal precipitates or fibrinous uveitis
- Occasionally bilateral "lumpy" renomegaly |
(1) Mature neutrophilia
(2) Hyperglobulinemia with polyclonal gammopathy
(3) IFP titer undependable & nonspecific |
(1) Pyogranulomatous
(2) Straw-colored, viscous, rarely chylous
(3) Cytology: moderate numbers of neutrophils, RBC, plasma cells, macrophages, lymphocytes, granular background |
(1) Thoracocentesis
(2) Supportive |
Grave |
|
Intravenous fluid overload |
Sudden onset of dyspnea in cats being Rx with IV fluids; muffled chest sounds; occasionally edema |
(1) Possible occult cardio- myopathy made apparent with fluid overload
(2) Possible coexisting anemia or hypoalbuminemia predisposing to fluid overload
(3) Sometimes purely iatrogenic from over zealous treatment |
(1) Pure transudate
(2) Clear
(3) Almost acellular on cytology |
(1) Thoracocentesis
(2) Judicious use of diuretics
(3) Give plasma or whole blood transfusion for hypoalbuminemia & anemia respectively |
Good if no serious underlying cause is present |
|
Acute trauma or bleeding disorders |
- Dyspnea
- Variable muffled chest sounds
- Other signs of trauma or sites or hemorrhage |
(1) Trauma-variable
(2) Coagulopathy - abnormal bleeding test parameters; i.e., prolonged PT, PTT, low platelet count
(2) Radiographs in trauma often denote fractured ribs & pulmonary contusion pattern |
(1) Blood red; defibrinated
(2) RBC & WBC proportions
similar to blood |
Trauma-depending on injury; usually conservative rest in the absence of other serious problems.
Coagulopathy--
(a) whole blood transfusion if severe
(b) cryoprecipitates
(c) vitamin K1, for warfarin intox. |
Usually good |
|
True chylothorax |
- Dyspnea
- Muffled chest sounds |
(1) Possible history of prior chest trauma
(2) Occasional lymphopenia
(3) Other causes include heart failure, heart worms, neoplasia |
(1) Milky white
(2) Cytology: normal lymphocytes, small # of RBC, smudge cells
(3) Orange staining chylomicrons with Sudan III
(4) Elevated triglycerides |
Surgical ligation of thoracic duct & anomalous lymphatics |
Fair to guarded |
|
Thoracic carcinomas or sarcomas |
- Dyspnea
- Muffled chest sounds
- Possible location of extra- thoracic source of neoplasia |
(1) Radiographs: demonstration of neoplasm
(2) Tissue biopsy confirmation if extrathoracic source is accessible |
(1) Usually serosanguineous
(2) Obstructive or inflammatory
(3) Cytology: RBC, mononuclear cells, mesothelial cells, anaplastic cells (variable presence) |
(1) Thoracocentesis
(2) Surgical removal if there is solitary mass
(3) Chemotherapy |
Guarded to grave |