Sterile pyogranulomatous nodular dermatitis

46 Sterile pyogranulomatous nodular dermatitis




INITIAL PRESENTATION


Nodules, alopecia and draining tract in an 18-month-old Labrador.



INTRODUCTION


Nodules are raised elevations of the skin, of 1 cm or more in diameter. Nodular or diffuse dermatitis and panniculitis are essentially histological diagnoses, characterized by the accumulation of inflammatory cells in the dermis or the subcutaneous tissue. The types of inflammatory cells include neutrophils, macrophages, eosinophils and lymphocytes. This accumulation may result from infectious or non-infectious causes, such as neoplasia, immune-mediated conditions, nutritional causes, blunt trauma or a sterile idiopathic process. A diagnosis of a sterile idiopathic process is made only when all other causes have been ruled out.




CASE PRESENTING SIGNS


An 18-month-old, neutered male Labrador was presented with a history of multiple nodules, draining tracts and erythema on the dorsum.



CASE HISTORY


Sterile nodular pyogranulomatous dermatitis in dogs usually has a spontaneous onset, with no history of trauma. Pain and pruritus are variable and, depending on the underlying trigger, systemic signs such as vomiting, abdominal pain and lethargy may be reported. Some dogs may be anorexic or have a depressed appetite.


The history in this case was:


• The nodules had a rapid onset, with history of pruritus at the site.

• There was no reported history of any previous dermatological disease.

• There was no contact with other animals and no history of trauma.

• A high-fibre diet (canine Hills r/d) was being fed because the dog was overweight.

• The dog was otherwise in good health.


CLINICAL EXAMINATION


Pyrexia, pain and a reluctance to move may be evident on physical examination. Single or multiple nodules are normally located on the trunk or on the neck. Nodules present deep within the subcutis would suggest a panniculitis. They may vary in size, ranging from a few millimetres to several centimetres in diameter. The nodules may be well demarcated or ill defined, and on palpation they may appear either soft and/or fluctuant, or hard. Some cases may have draining tracts that release a purulent or even oily exudate (in the case of panniculitis) of variable colour.


In this case:


• Physical examination was within normal limits.

• Multiple ill-defined nodules were present on the dorsal lumbar area. There was no evidence of pain on nodule palpation.

• Erythema, scarring and sinus tracts were evident when the fur was clipped (Fig. 46.1) over affected areas.

• There was a yellowish to red coloured exudate discharging from sinus tracts.

image

Figure 46.1 Raised swelling with erythema, scarring and depigmentation is evident when the fur was clipped. Note a pinpoint draining tract.




DIFFERENTIAL DIAGNOSES


Ill-defined nodules with discharging sinus tracts can occur due to a number of conditions, and the differential diagnoses in this case included:



• Deep folliculitis and furunculosis

• Bacterial or fungal pseudomycetoma

• Opportunistic mycobacterial infection

• Subcutaneous mycoses

• Cutaneous cysts

• Sterile pyogranulomatous nodular dermatitis and/or panniculitis

• Xanthomatosis

• Cutaneous histiocytosis

• Multiple cutaneous histiocytomas.

Other causes of nodular disease which were unlikely differentials in view of the signalment and clinical lesions included injection site reaction, foreign body reactions, abscess formation and cutaneous neoplasia including epitheliotropic lymphoma and mast cell tumour.



CASE WORK-UP


It is essential to systematically and carefully rule out all the other differential diagnoses in order to make a diagnosis of idiopathic sterile pyogranulomatous dermatitis. In any nodular disease, cytological examination of fine-needle aspirates and/or impression smears of exudate is indicated. A pyogranulomatous inflammation (neutrophils and macrophages) and an absence of microorganisms will be seen in cases of sterile pyogranulomatous disease. Biopsied specimens are essential for bacterial and fungal cultures, and also for histology. Either an excision biopsy of a nodule or a wedge biopsy of a larger lesion should be taken for this purpose. Special staining techniques of histological sections can help to rule out the presence of bacterial and fungal organisms. Ziehl–Neelsen (ZN) stain may reveal acid-fast bacteria such as Mycobacteria and Nocardia. Other bacteria may be identified by their Gram-staining properties. Periodic acid–Schiff (PAS) stain and Gomori’s silver stain are used to identify the presence of fungal elements.


As nodular skin disease is sometimes associated with systemic conditions, haematology and biochemistry, including serum amylase and pancreatic-specific lipase, are indicated, especially if gastrointestinal signs or abdominal signs are present. If pancreatic disease is suspected, abdominal ultrasonography and radiography, followed by exploratory surgery, may be necessary.


In this case the following tests were performed:


• Cytological examination of smears of the exudate, stained with modified Wright’s stain, revealed pyogranulomatous inflammation with fat necrosis (Fig. 46.2a, b).

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Sep 3, 2016 | Posted by in SMALL ANIMAL | Comments Off on Sterile pyogranulomatous nodular dermatitis

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