Articles

Case of the Month: Trunk Predominant Pemphigus foliaceus

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Annika Herrmann

Board Certified Anatomic Pathologist

Sukie, a 12 year old female intact cross breed dog

Clinical history

Sukie presented with multiple highly pruritic lesions on the dorsum between the thoracic and lumbar spine and some smaller lesions distributed across the back over the last 2 months. Some lesions resolved with antibiotic treatment, while others remained. She had a bout of similar lesions in the previous year. The submitting vet suspected furunculosis.

Histology

Multiple large pustules filled with eosinophils and degenerate and non-degenerate neutrophils were found predominantly in the infundibula of hair follicles, but also in the epidermis. The pustules contained numerous acantholytic keratinocytes and occasionally rafts of detaching keratinocytes. This was associated with a predominantly eosinophilic and neutrophilic mural folliculitis and peri folliculitis, as well as reactive epidermal hyperplasia.

 Figure 1: Hair follicle; note extensive intrainfundibular pustule.

Figure 2: Intrainfundibular pustule filled with numerous eosinophils (examples: green arrow head) and acantholytic keratinocytes (examples: blue arrow heads); also note raft of detaching keratinocytes (red arrow head).

Figure 3: Higher magnification of follicular wall; note numerous eosinophils (green arrow head) and neutrophils (blue arrow head) in the perifollicular dermis and eosinophils (yellow arrow head) in the follicular wall.

Figure 4: Large intracorneal pustule in the epidermis.

Figure 5: Higher magnification of epidermal pustule; note numerous acantholytic keratinocytes (yellow arrow heads).

Interpretation

Trunk-predominant pemphigus foliaceus

Note that due to the observation of numerous eosinophils in the inflammatory infiltrate and the follicle-centric inflammation, eosinophilic furunculosis was considered, which can sometimes be observed in skin areas other than the face. However, the very obvious acantholysis and lack of follicular destruction observed in this case suggested this is unlikely.

Some information on Pemphigus foliaceus and trunk-predominant Pemphigus foliaceus

Pemphigus foliaceus (PF) is an autoimmune skin disease that is characterized by the production of autoantibodies against a component of the adhesion molecules on keratinocytes causing the cells to detach from each other within the superficial epidermal layers (acantholysis). PF is the most common autoimmune skin disease in dogs and cats. There is no proven age, sex, or breed predisposition, but among dogs, Akitas and Chow Chows may be predisposed. PF is usually idiopathic, but some cases may be drug induced, or may occur as a sequel to a chronic inflammatory skin disease.

The primary lesions are superficial pustules. Intact pustules can be difficult to find because they are fragile and rupture easily. Secondary lesions include superficial erosions, crusts, scales, epidermal collarettes and alopecia. The disease often begins on the bridge of the nose, around the eyes, and on the ear pinnae, before it becomes generalized. Nasal depigmentation frequently accompanies facial lesions. Skin lesions are variably pruritic and may wax and wane. Footpad hyperkeratosis is common and in some dogs and cats, this is the only symptom. Mucocutaneous involvement is usually minimal in dogs. In cats, lesions around the nail beds and nipples are a unique and common feature of pemphigus.

In this particular case, the distribution of the lesions was restricted to the trunk, consistent with the recently described trunk-predominant PF. This is a variant of PF that presents without muzzle/ nasal planum involvement and sometimes without footpad involvement. This variant is thus more difficult to differentiate from superficial bacterial pyoderma. The histopathological features in trunk-predominant PF are generally similar to those in ‘conventional’ PF. Involvement of hair follicles is described in both trunk-predominant and ‘conventional’ PF and may be prominent in facial PF. A predominance of follicular lesions has not been described for trunk-predominant PF so far and may be a unique feature in this case.

Possible differential diagnoses based on clinical picture

Differentials include demodicosis, superficial pyoderma, dermatophytosis, other autoimmune skin diseases, subcorneal pustular dermatosis, eosinophilic pustulosis, drug eruption, dermatomyositis, zinc-responsive dermatosis, cutaneous epitheliotropic lymphoma, superficial necrolytic migratory erythema, and mosquito bite hypersensitivity (in cats).

 Diagnosis

  • Rule out other differentials.
  • Cytology (pustule): neutrophils and acantholytic cells are seen. Eosinophils may also be present.
  • Antinuclear antibodies (ANA): negative, but false positives are common.
  • Histopathology: intra-/ subcorneal pustules containing neutrophils and acantholytic cells, with variable numbers of eosinophils
  • Immunofluorescence (skin biopsy specimens): detection of intercellular antibody deposition is suggestive, but false-positive and false-negative results are common. Positive results should be confirmed histologically
  • Bacterial culture (pustule): usually sterile, but occasionally bacteria are isolated if secondary infections are present

Histology sampling with suspected PF

Make sure that intact pustules are collected, otherwise the diagnostic features of the disease will be obscured by erosion and ulceration of the epidermis. Choose a punch biopsy instrument that is wide enough to capture the pustule in its entirety, otherwise the roof of the pustule will float off. If this is not possible, take an ellipse/ wedge biopsy.

References

Gedon et al.: Histopathological characterisation of trunk-dominant canine pemphigus foliaceus, and comparison with classic facial and insecticide-triggered forms. Vet Derm (2023). DOI: 10.1111/vde.13174

Medlau and Hnilica: Small animal Dermatology. A Color Atlas and  Therapeutic guide. 2nd edition (2006).