Diagnosis is made by a combination of history, clinical signs and biopsy. It is important to rule out other diseases that may appear similar. Some of these include demodicosis, angioedema, severe bacterial infection, pemphigus foliaceous, drug eruption and sterile nodular panniculitis. Your veterinarian may recommend the following: Complete blood counts (CBC). This test may reveal a high white blood cell count and anemia.
Deep skin scrapings. It is important to rule out demodicosis, which could also cause similar signs. Demodicosis occurs in young animals and treatment with steroids would be contraindicated. This test is recommended in all puppies with skin disease.
Cytology of the aspirate of pustules or abscesses. This test may reveal many white blood cells without bacteria. Staphylococcus may be isolated from draining lesions but intact abscesses and lymph nodes are usually negative for bacterial growth.
Cytology of the aspirates of joints. In dogs with joint pain, this test reveals infective arthritis with no bacteria and the aspirates are usually negative for bacterial growth on culturing.
Multiple biopsies from fresh, intact lesions
Skin samples should be used for both histopathology and cultures. The inflammation may be so severe that the normal dermal architecture is destroyed, including hair follicles and glands.
When secondary infection is present, neutrophils becomes the prevalent cell. The infiltrate surrounds the hair follicles forming large granulomas. In severe and more chronic cases, the inflammation may be very deep. The same inflammatory process may be seen in lymph nodes, even when anatomically distant from the site of apparent disease.
Tissue samples should be submitted for cultures (aerobic, anaerobic, fungal and mycobacterial) to confirm the sterile nature of the disease and ensure that an infection isn't missed.
Mycobacterial infections are not commonly seen at such a young age but may cause severe dermatitis. Special staining (acid fast stain) should be used to detect the organisms on histopathology. Most organisms would grow rapidly (within 7 days) on appropriate media.
Demodicosis may present with similar histopathological changes but usually fragments of mites can be identified in the center of the granulomas.
Pemphigus foliceous (immune skin disease) has been reported to occur in young animals. In those cases, pustules are seen on face and ears. Lymph nodes may be enlarged but usually not to the extent seen in puppy strangles. Animals may feel depressed and lethargic.