Urticarial allergic reaction in a dog

This is a skin biopsy from a 3-year-old Jack Russell Terrier. The dog developed a generalised erythematous rash and limb oedema within 36 hours of antibiotic and anti-inflammatory treatment for a bout of vomiting and diarrhoea.

Fig 1. In sections of haired skin, the epidermis is intact and the superficial perivascular to interstitial dermis contains a multifocal, moderate cellular infiltrate (arrows) accompanied by mild dermal oedema.
Fig 2. The cellular infiltrate is dominated by eosinophils (arrow). The endothelium lining the dermal blood vessels (bv) is consistently plump.

Final Diagnosis

Superficial perivascular to interstitial eosinophilic dermatitis


The histopathology together with the clinical history is consistent with urticarial allergic eruption, associated with a hypersensitivity reaction. It is not cause-specific but an adverse drug reaction is one of the most commonly reported causes and was suspected in this particular case. Other causes include insect/arthropod bites, vaccines and food allergy.