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Basics ⬇

Outline

BASICS

Definition!!navigator!!

A sudden, forceful, noisy expulsion of air through the glottis to clear mucus and particles from the tracheobronchial tree and glottis.

Pathophysiology!!navigator!!

  • This reflex is a protective respiratory defense mechanism that, together with the mucociliary escalator, clears undesired material from the tracheobronchial tree proximal to the level of segmental bronchi
  • Initiated by stimulation of irritant receptors that ramify between epithelial cells from the level of the larynx down to the distal bronchioles and by receptors located in the lung parenchyma and pleura
  • Receptors are stimulated by mechanical deformation, chemically inert dust particles, foreign bodies, pollutant gases, exposure to cold or hot air, inflammatory conditions, excessive mucus or exudates, and chemical mediators such as histamine
  • Most of the afferent impulses travel in the vagus nerve, but also in the glossopharyngeal, trigeminal, and phrenic nerves, to cough centers in the medulla oblongata

Systems Affected!!navigator!!

  • Respiratory
  • Musculoskeletal
  • Cardiovascular
  • Nervous

Incidence/Prevalence!!navigator!!

  • Mostly unknown
  • Among horses without acute respiratory infection, prevalence of cough at rest or during exercise is reported to vary between 10% and 50 %, depending on the study population

Geographic Incidence!!navigator!!

Worldwide

Signalment!!navigator!!

  • All ages, breeds, and sexes
  • Cough resulting from viral or bacterial infections is more common in weanlings and yearlings while cough associated with equine asthma or other chronic conditions is observed in more mature horses

Signs!!navigator!!

Historical Findings

  • Season and activity
    • Cough associated with equine asthma typically has a higher incidence when horses are confined indoors, except for the summer form of equine asthma (summer pasture-associated equine asthma)
  • Housing and feeding practices
    • Cough associated with equine asthma is exacerbated by exposure to hay and straw and poor ventilation; however, cough from other causes can also be exacerbated by inhaled irritants
    • Silicosis typically occurs in horses fed on the ground or grazed in dusty paddocks in areas such as the Monterey Peninsula of California, which have exposed cristobalite silica shale
  • Speed of onset, contagiousness, duration
    • Sudden onset and rapid spread are characteristics of viral infections
    • Cough associated with lungworms also typically has a sudden onset and may affect multiple horses, but it tends to become chronic, while viral infections typically do not
    • Cough associated with foreign body or food aspiration into the tracheobronchial tree is sudden in onset but does not spread to affect other horses
    • Gradual onset and chronic course are typical for equine asthma, interstitial pneumonia, fungal pneumonia, and thoracic neoplasia
    • Exercise frequently precipitates cough caused by many conditions, particularly those associated with airway irritation or fluid accumulation in airways

Physical Examination Findings

  • Fever—usually indicates an infectious cause. Low-grade fever can be present with neoplasia (e.g. lymphoma)
  • No fever—typically found in equine asthma, upper airway abnormalities (other than retropharyngeal abscess), parasitic pneumonia, exercise-induced pulmonary hemorrhage, and some neoplasia (e.g. bronchial carcinoma)
  • Food return via the nose—typically indicates esophageal obstruction, aspiration of food secondary to anatomic or neurologic derangement in the upper airway, severe pharyngeal inflammation, or cleft palate
  • Pleurodynia—typically occurs with pleuropneumonia, less commonly with noninfectious pleural inflammation
  • Nasal discharge—reflects disease characterized by exudation or drainage of mucus or purulent exudate from the lower airways, nasopharynx, guttural pouches, nasal passages, or paranasal sinuses
  • Harsh, persistent cough suggests involvement of the major airways or exudate in the large airways secondary to pulmonary disease
  • Soft, infrequent cough often reflects equine asthma, interstitial lung disease, or pulmonary edema secondary to cardiac failure

Causes!!navigator!!

Most coughs are initiated by stimulation of receptors in the trachea and bronchi; therefore, cough is more likely to originate from diseases involving the lower respiratory tract.

Lower Respiratory Tract Diseases

  • Bronchial—inflammation, infection, allergy/hypersensitivity, foreign body, and tumor
  • Pulmonary—inflammation, infection, aspiration pneumonia, pulmonary edema, tumor, acute bronchointerstitial pneumonia, pneumoconiosis, and granulomatous pneumonia
  • Pulmonary vascular—thrombosis/embolism, congestive cardiac failure, and pulmonary hypertension
  • Pleural—inflammation, infection, hernia, and tumor

Upper Respiratory Tract Diseases

  • Nasopharyngeal—pharyngitis, nasopharyngeal foreign body, cyst, or tumor; strangles, cleft palate, dorsal displacement of the soft palate, guttural pouch empyema, tympany, or mycosis (secondary to aspiration)
  • Laryngeal—hemiplegia with dynamic collapse, inflammation/chondritis, epiglottic entrapment or ulcer, foreign body, tumors, previous laryngeal surgery
  • Tracheal—inflammation, foreign body, smoke or chemical irritation, collapse, and tumor
  • Dysphagia from any cause resulting in food aspiration

Risk Factors!!navigator!!

See the individual conditions causing cough.

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

Differentiating Similar Signs

Cough is not easily confused with other signs.

Differentiating Causes

See Historical Findings, Physical Examination Findings, and Risk Factors.

CBC/Biochemistry/Urinalysis!!navigator!!

  • Neutrophilia, hyperfibrinogenemia, and elevated serum globulin concentration are common in bacterial infections and some malignant tumors
  • Lymphopenia and lymphocytosis are common in viral infections
  • Eosinophilia is a common finding in lungworm infection and some horses with granulomatous interstitial lung disease

Imaging!!navigator!!

  • Thoracic radiography for differentiating types of lower respiratory tract disorders (consolidation, mass lesions, infiltrative interstitial disease, and pleural effusion)
  • Thoracic ultrasonography in patients with superficial pulmonary consolidation, pleural disease, or mediastinal mass
  • Radiography of the upper airways and proximal esophagus
  • Echocardiography if primary cardiac disease or right heart disease secondary to a pulmonary condition is suspected

Other Diagnostic Procedures!!navigator!!

  • Arterial blood gases in patients with signs of respiratory distress
  • Visual inspection of the upper airways, guttural pouches, trachea, and bronchi with endoscopy. If indicated, the pleural space can be visualized by thoracoscopy
  • Biopsy specimens of lesions or airway walls can be collected via endoscopy, transcutaneous lung biopsy, or thoracoscopy
  • Collection of nasopharyngeal swabs or washes from horses with acute-onset cough and fever help to establish the diagnosis of acute viral infection and strangles (for culture and PCR)
  • Transtracheal or transendoscopic aspiration with cytology and culture for evaluation of infectious (and some inflammatory) lower respiratory tract disorders
  • Bronchoalveolar lavage with cytology for evaluation of lower respiratory tract disorders (equine asthma, silicosis, and granulomatous lung disease)
  • Thoracocentesis with cytologic evaluation and culture of aspirated fluid
  • Direct and flotation fecal tests (e.g. Baermann) to detect ova or larvae of respiratory parasites and ascarids. Testing of donkeys or mules co-grazed with affected horses
  • Echocardiography and ECG in patients with suspected cardiac disease

Treatment ⬆ ⬇

Outline

TREATMENT

Aims!!navigator!!

  • Based on the underlying cause
  • Regardless of the cause, decrease stimulation of irritant receptors

Appropriate Health Care!!navigator!!

Horses presented with cough usually are evaluated as outpatients but the presence of respiratory distress, pleural effusion, congestive cardiac failure, or other features of a serious disease process are indications for hospitalization.

Nursing Care!!navigator!!

Horses with suspected viral respiratory disease and contacts in the same airspace should be isolated as a group. Do not allow other horses to enter the same airspace occupied by sick horses.

Activity!!navigator!!

Exercise restriction is best until a cause for the cough is established and corrected, especially when activity aggravates the cough.

Housing and Diet!!navigator!!

Regardless of the cause, decrease inhalation of dust, cold air, or noxious gas. For pharyngeal conditions, soft and moist diet can decrease mechanical irritation of the nasopharynx.

Client Education!!navigator!!

Inform owners that a wide variety of conditions can be responsible for the cough and that an extensive workup may be required to define and treat the underlying cause.

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

Treatment is directed at the underlying cause rather than at attempting symptomatic relief by using cough suppressants.

Contraindications!!navigator!!

  • In general, avoid using corticosteroids unless an allergic-type disease or airway hyperreactivity is suspected, and evidence of infection or parasitic infestation is lacking
  • Foals with acute respiratory distress syndrome (i.e. acute bronchointerstitial pneumonia) may benefit from corticosteroids even when an underlying infectious cause is present
  • Do not use cough suppressants in patients with heart disease or when a respiratory infection is present (unless infection is under control and cough is causing significant discomfort)

Precautions!!navigator!!

  • Cough suppressants—indiscriminate use may obscure warning signs of serious pulmonary or cardiac disorders
  • Bronchodilator therapy may exacerbate hypoxemia in patients with ventilation–perfusion mismatch
  • NSAIDs may mask fever and pleurodynia

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

Cough may persist for several weeks after resolution of other signs in horses with infectious respiratory disease because restoration of normal structure and function in the respiratory mucosa takes several weeks.

Prevention/Avoidance!!navigator!!

Contingent on diagnosis.

Possible Complications!!navigator!!

Some diseases that cause cough also can induce prolonged or permanent respiratory dysfunction and even death.

Expected Course and Prognosis!!navigator!!

Contingent on diagnosis.

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Age-Related Factors!!navigator!!

See Historical Findings.

See Also!!navigator!!

Abbreviations!!navigator!!

  • NSAID = nonsteroidal anti-inflammatory drug
  • PCR = polymerase chain reaction

Suggested Reading ⬆ ⬇

Kohn CW. Cough. In: Reed SM, Bayly WM, Sellon DC, eds. Equine Internal Medicine, 3e. St. Louis, MO: WB Saunders, 2010:122–126.

Korpas J, Tomori Z. Cough and other respiratory reflexes. Prog Respir Res 1979;12:15–18.

Korpas J, Widdicombe JG. Aspects of the cough reflex. Respir Med 1991;85(Suppl. A):3–5.

Wasko AJ, Barkema HW, Nicol J, et al. Evaluation of a risk-screening questionnaire to detect equine lung inflammation: results of a large field study. Equine Vet J 2011;43:145–152.

Wilson WD, Lofstedt J, Lakritz J. Cough. In: Smith BP, ed. Large Animal Internal Medicine, 5e. St. Louis, MO: Elsevier Mosby, 2015:40–48.

Author(s) ⬆

Authors: Mathilde Leclère and W. David Wilson

Consulting Editors: Mathilde Leclère and Daniel Jean