This condition affects dogs of any age or breed, although German shepherds are predisposed. It affects the mucocutaneous junctions
(MCJs) of the nose and lips most frequently, but other MCJs can also be affected. This is a surface bacterial infection (usually
S. pseudintermedius) wherein there is a "standoff" between the bacteria and the immune system at the MCJ. Intially, there
is erythema and swelling of the nose near the nasal sulci. Crusts then form followed by fissuring and erosion in some cases.
A purulent discharge is often present and the crusting can extend to the dorsal aspect of the nasal planum (NP). DLE is the
most common ddx and it can be difficult to distinguish between these two diseases clinically and histologically. Therefore,
prior to a nasal biopsy, it is essential to eliminate any bacterial infection in order to give a pathologist a clearer picture
of the primary disease. Treatment with topical antibiotics such as mupirocin, and topicals plus systemic antibiotics in more
severe cases is highly effective. If recurrence is seen, topical mupirocin 2-3 times per week may be helpful for maintenance.
Discoid lupus erythematosus (DLE)
DLE is the second most common immune-mediated dermatitis of the dog. It is very rare in the cat. It is one of the most benign
of the immune-mediated diseases and there is no systemic involvement. Ultraviolet light exposure aggravates this condition
in the majority of cases. The lesions usually begin on the NP and may extend up the bridge of the muzzle. It may also affect
Pemphigus erythematosus (PE), pemphigus foliaceus (PF) and pemphigus vulgaris (PV) are all pustular and crusting autoimmune
diseases that often affect the NP and can occur in dogs and cats. PE is the most likely of these to start near the nose. However,
it usually begins on the haired skin (bridge of the nose) and then spreads rostrally to the NP. Clinically and histologically,
it shares features of DLE and PF. Pustules, crusts, and alopecia are often seen on the haired skin of the muzzle. On the NP,
crusts often form on the dorsal aspect and depigmentation, erosions, and ulcers with a loss of the normal cobblestone architecture
on the rostral aspect of the NP occur. PE is almost always limited to the face, nose, and pinnae.
PF may start on the muzzle and NP, although it will soon begin to affect other body surfaces such as the footpads and trunk
in most cases. Some cases of PF start on the trunk.
PV is a very rare disease that is a deeper form of pemphigus. Nasal lesions are often characterized by erosions and ulcers
and there are oral lesions in 90% of cases.
The diagnosis of the above diseases is based upon examination, cytology, and histopathology. Treatment is accomplished through
immunosuppresion (corticosteroids, azathioprine, etc.) and photoprotection, and is needed lifelong in most cases.