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Case Report: Pyrexia of Unknown Origin in a 12-year-old Weimeraner

A 12-year-old, neutered, female Weimeraner presented with a history of pyrexia of two month’s duration. Previous treatment with clavulanate/amoxicillin had temporarily resolved the pyrexia, but this had recurred as soon as treatment was stopped. Three months previously, the dog had had a single episode of cystitis. An episode of vulval discharge had also been noted at one examination. She was being successfully treated for urinary incontinence with Propalin. One month previously a disorganised mass had been removed from the left chest, which had been histologically diagnosed as an infiltrative lipoma.

Physical examination

The dog was bright and well. She had a temperature of 104.5ºF and a heart rate of 140. A grade iv/vi heart murmur was present. Colour and capillary refill time were good. There was a mucoid vulval discharge present. Abdominal palpation was unremarkable. On her left chest were multiple small skin nodules, one of which was discharging.

Problem list

  • Pyrexia
  • Vulval discharge
  • Nodules on chest
  • Heart murmur

Differential diagnosis

PUO has a multitude of differential diagnoses, broadly classified as infectious, immune-mediated, neoplastic and miscellaneous. The approach to this case involved ascertaining whether the pyrexia was related to the discharging skin nodules, the vulval discharge, the heart murmur or something else entirely.


Routine haematology and biochemistry were unremarkable except for a mild neutrophilia. Chest radiography was unremarkable, with the heart size in normal limits. Ultrasonography of the heart revealed a slightly dilated left ventricle and thickened interventricular septum. There was no evidence of bacterial endocarditis. Plain abdominal radiography, pneumocystography, double contrast cystography and ultrasonography demonstrated a thickening of the bladder wall. The bladder neck was markedly intrapelvic. Urinalysis demonstrated numerous bacterial rods with large numbers of white blood cells. Exploratory laparotomy was carried out to ascertain the nature of the bladder thickening, and to rule out any other intra-abdominal causes of pyrexia. A full-thickness bladder wall biopsy was taken which revealed a septic inflammatory response.

The left chest wall mass was removed, and analysed for bacterial culture and sensitivity and histology. The mass was described histologically as a trichogranuloma, which is a foreign body reaction to hair. E. coli sensitive to clavulanate/amoxicillin, was grown in the urine and Staph intermedius resistant to ampicillin, but sensitive to enrofloxacin and clavulanate/amoxicillin, was cultured from the chest mass.


The dog was discharged with instructions to take a three-month course of enrofloxacin. Both bacterial isolates were sensitive to enrofloxacin and clavulanate/amoxicillin in vitro, but since the pyrexia had not responded to clavulanate/amoxicillin in vivo, enrofloxacin was chosen instead.


The dog responded well to initial treatment, is normothermic, and is now being managed by the referring vets with intermittent cystocentesis and appropriate bacterial cover.


The investigation of PUO can be lengthy and sometimes frustrating. If more than one condition is present it can be difficult to know which, if any, is responsible for the fever. The general approach to a case of PUO is to persue a logical and systematic search for a cause of pyrexia, starting with investigating any obvious abnormalities, and then widening the search if necessary to apparently normal systems.

In this case, the presence of a severe bacterial cystitis suggested that this was the likely source of the pyrexia. The skin mass, although infected, seemed too small to be producing a high temperature for such a prolonged period.

The probable reason that the bacterial cystitis had not responded to initial antibiotic therapy is that the intra-pelvic bladder neck had weakened the bladder defences, allowing an ascending bacterial infection. Long term antibiotics are often needed to treat established and complicated cases of bacterial cystitis, and in this case, since continued ascending infection will be likely, it may be that lifelong prophylactic antibiotics will be necessary.