A retrospective study comparing the histopathological features and response to treatment in two canine nasal dermatoses, DLE and MCP.

Canine discoid lupus erythematosus (DLE) and mucocutaneous pyoderma (MCP) have overlapping clinical and histopathological changes, often making diagnosis difficult. Histopathological features of 27 nasal planum biopsies were scored to determine whether DLE and MCP were histopathologically distinguishable. Long-term follow-up, enabling assessment of clinical diagnoses, was available on 15 cases; 11/15 cases were immunomodulatory responsive (ImR) and 4/15 were antibiotic responsive (AbR). Clinical diagnosis, determined by response to treatment for 15/27 cases, was not predictable based on scoring of histopathological features. Distinct histopathological patterns were observed: 2/11 ImR cases had a lymphocyte-rich interface dermatitis. All other cases had the same histopathological changes: a band-like diffuse superficial plasmacytic to lymphoplasmacytic dermatitis +/- focal basal cell damage, but different clinical diagnoses (4/4 AbR, 9/11 ImR). German shepherd dogs/crosses were over-represented (44.4% of the cases) and tended to have more multifocal lesions (41.7% vs. 26.7% of all other breeds). Longer duration of disease was associated with a preponderance of plasmacytic infiltrate (P = 0.026).