JPC SYSTEMIC PATHOLOGY
INTEGUMENTARY SYSTEM
September 2022
I-M17 (NP)

Signalment:  A three-year-old spayed female mixed breed dog

 

HISTORY:  This dog had nodular eruptions over the muzzle and around the nares. 

 

HISTOPATHOLOGIC DESCRIPTION:  Haired skin: Infiltrating and expanding the dermis; elevating the epidermis; and surrounding, separating, and replacing the adnexa are multifocal to coalescing, densely cellular inflammatory infiltrates that track linearly along hair follicles and form poorly defined, elongate nodules up to 2 mm in length. The nodules are composed of abundant macrophages, epithelioid macrophages, lymphocytes, plasma cells, neutrophils, and rare multinucleated giant cells admixed with plump fibroblasts and a small amount of loose collagenous connective tissue (fibrosis). Multifocally the dermis contains foci of hemorrhage, fibrin and edema that separate dermal collagen fibers. The overlying epidermis has an increased amount of granular brown pigment (hyperpigmentation). There are occasional ectatic apocrine glands and lymphatics with dermal blood vessels lined by hypertrophied endothelium (reactive).

 

MORPHOLOGIC DIAGNOSIS:  Haired skin:  Dermatitis, periadnexal and nodular, granulomatous, multifocal to coalescing, moderate, mixed breed, canine.

 

ETIOLOGIC DIAGNOSIS:  Idiopathic granulomatous dermatitis

 

CONDITION:  Sterile granuloma/pyogranuloma syndrome (SPGS)

 

SYNONYM:  Periadnexal multinodular granulomatous dermatitis (PMNGD)/ Pyogranuloma syndrome; Idiopathic sterile granuloma/pyogranuloma

 

GENERAL DISCUSSION: 

• Uncommon condition in dogs, rare in cats and horses
• Diagnosis by exclusion of infectious causes of pyogranulomatous dermatitis
• No sex or age predisposition
• May spontaneously resolve after several months in dogs

 

PATHOGENESIS:

• Cause unknown - Likely immune-mediated due to:
  • Negative tissue cultures, negative special stains for infectious agents, absence of foreign material, response to immunomodulatory therapy

 

TYPICAL CLINICAL FINDINGS:

• Dogs:
  • Single or multiple, firm, non-pruritic, well demarcated, partially alopecic nodules or plaques
  • Lesions may be found anywhere; face and distal extremities most common
  • Collies, Boxers, Great Danes, Weimaraners, English Bulldogs, Doberman Pinschers, Dachshunds, Golden Retrievers predisposed
• Cats:
  • Lesions usually symmetrical and pruritic; purple or orange-yellow, and may turn red to purple when palpated
  • Lesions predominate on the head, especially periauricular or on pinna; less often on paws and trunk
• Horses:
  • Generally asymptomatic
  • Typically solitary nodules on lip, eyelid, or pastern, or multiple lesions scattered over the body

 

TYPICAL GROSS FINDINGS:

• Single or multiple, localized or generalized, firm, haired to partially alopecic, erythematous papules, nodules, and plaques
• May ulcerate and develop secondary infections

 

TYPICAL LIGHT MICROSCOPIC FINDINGS: 

• Large perifollicular granulomas or pyogranulomas that are elongated, vertically oriented, and track hair follicles but do not invade them
• Histiocytes, lymphocytes, and neutrophils predominate with occasional plasma cells and/or multinucleated giant cells.
• Cats may have many multinucleated giant cells
• Older lesions may be diffuse, efface adnexa, and extend into subcutis
• Inflammatory infiltrate is devoid of foreign material or infectious agents detected by routine techniques (polarization, special stains)

 

ADDITIONAL DIAGNOSTIC TESTS:  

• Multiple biopsies using sterile technique for aerobic, anaerobic, fungal and mycobacterial culture and/or special stains (B&B, B&H, GMS, PAS) and/or PCR to rule out infectious etiologies, especially Leishmania and Mycobacterium

 

DIFFERENTIAL DIAGNOSIS:

• Cutaneous neoplasms
• Bacterial, fungal, algal, protozoal, parasitic or foreign body granulomatous dermatitis; especially Leishmania and Mycobacterium
• Reactive histiocytosis
• Canine juvenile cellulitis
• Canine cutaneous histiocytoma
• Sterile nodular panniculitis

 

 

COMPARATIVE PATHOLOGY: 

• Horses: Equine idiopathic generalized or systemic granulomatous disease (sarcoidosis) is a rare disease with three clinical presentations; cause is unknown
  • Localized:  localized, non-pruritic, exfoliative dermatitis on 1 or 2 lower limbs; variable pain, edema, and lameness
  • Partially generalized: above findings and/or cutaneous/subcutaneous nodules on a small area of the body; may see peripheral lymphadenopathy
  • Generalized: above findings with one or more of the following signs: fever, exercise intolerance, pain when touched, respiratory distress, weight loss, and/or peripheral lymphadenopathy
  • Histo lesions: multifocal, nodular to diffuse lymphogranulomatous dermatitis with multinucleated giant cells; vasculitis may be seen

 

REFERENCES: 

1. Gross TL, Ihrke PJ, Walder EJ, Affolter VK. Skin Diseases of the Dog and Cat: Clinical and Histopathologic Diagnosis. 2nd ed. Oxford, UK: Blackwell Publishing Co.; 2005: 410-415.
2. Mauldin EA, Peters-Kennedy J. Integumentary system.  In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 6th ed. St. Louis, MO: Elsevier; 2016:700-701.
3. Rosa FB, Older CE, et al. Analysis of Bacterial and Fungal Nucleic Acid in Canine Sterile Granulomatous and Pyogranulomatous Dermatitis and Panniculitis. Vet Pathol. 2018; 55(1):124-132.
4. Schissler J. Sterile Pyogranulomatous Dermatitis and Panniculitis. Vet Clin North Am Small Anim Pract. 2019; 49(1):27-36.
5. Scott DW, Miller WH, Griffin CE. In: Muller & Kirk’s Small Animal Dermatology. 6th ed. Philadelphia, PA: WB Saunders Company; 2013:1136-1140.
6. Welle MM, Linder KE. The Integument. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 6th ed., St. Louis, MO: Elsevier; 2022: 1189-1190.

Click the slide to view.

---