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EQUINE VETERINARY EDUCATION / AE / FEBRUARY 2018


Nasal culture, polymerase chain reaction (PCR) and serological blood tests for strangles infection are often initially used to diagnose strangles and clinicians are often reluctant to perform upper airway endoscopy at this stage, because of the expense of dealing with the inevitable contamination of equipment and clothing and knowing that most cases will resolve without such intervention. Molecular analysis (e.g. PCR) and/or bacterial culture of nasal swabs may confirm strangles, or indicate an alternative pathogen such as found in the accompanying case report (DeLoache et al. 2018). In cases of more persistent nasal discharge, endoscopy of


the upper airway is required, initially to assess if other causes of unilateral nasal disease are present, such as sinusitis, nasal conchal bulla infection or infection of the rostral maxillary cheek teeth with nasal drainage. Endoscopy of the guttural pouch area may show exudate draining from one or both ostia and/or compression of the nasopharyngeal roof, that often appears bilateral even in cases of unilateral guttural pouch distension (Fig 7). Passage of the endoscope into the guttural pouch via


Fig 5: Endoscopic image of the roof of the nasopharynx of a horse that presented with chronic, mainly left-sided nasal discharge. This image shows the nasopharyngeal recess that contains a nasopharyngeal-guttural pouch fistula. Chondroids are visible within the left guttural pouch that cannot drain through the small fistula, ensuring persistent infection of this guttural pouch.


Confirmation of diagnosis


Cases of guttural pouch empyema may have a history of contact with strangles-infected horses and such cases may initially have a bilateral purulent nasal discharge, which later becomes unilateral, if empyema develops in just one guttural pouch. Initially, affected horses may have painful swelling of the submandibular and parotid area lymph nodes, abnormal head and neck carriage. Stertor and dysphagia can develop if gross distension of pouches occur due to empyema (Fig 6), or to swollen retropharyngeal lymph nodes in acute cases.


the nasopharyngeal ostium may show purulent exudate or chondroids (or both) lying on the guttural pouch floor. Samples of exudate can be collected for culture and/or PCR analysis for evidence of strangles. Standing, lateral radiographs can also be used to assess for fluid lines or chondroids within the guttural pouches, but it is not always possible to radiographically ascertain whether unilateral or bilateral GP disease is present (Fig 6).


Treatment


Lower grade guttural pouch empyema can be treated conservatively by postural drainage, including isolation of such cases if infectious disease is suspected. Nonresponding cases can have guttural pouch lavage as described by DeLoache et al. (2018) and this can be performed using an indwelling commercially available guttural pouch catheter, a Foley or custom-made catheter, or transendoscopically. Lukewarm saline is the treatment of choice as added antiseptics will cause inflammation of the guttural pouch mucosa which may hinder drainage. If persistent infection remains following saline


Fig 6: Marked guttural pouch empyema. a) Endoscopic view of the caudal nasopharynx and larynx showing collapse (arrows) of the nasopharyngeal roof and some laryngeal obstruction. b) This lateral radiograph shows extreme distension of the guttural pouch (arrows) with a fluid line dorsally (single arrow, blue outline), great compression on and narrowing of the nasopharyngeal lumen ventrally (single arrow) and caudal distension of the GP towards the neck (horizontal arrows).


© 2016 EVJ Ltd


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