JPC SYSTEMIC PATHOLOGY
Signalment (JPC #2237039): 2-year-old shar-pei
HISTOPATHOLOGIC DESCRIPTION: Haired skin: Diffusely, throughout the dermis, collagen bundles are fragmented, distorted, and widely separated by abundant, wispy, amphophilic material (mucin) and increased clear space (edema) admixed with few neutrophils, macrophages, lymphocytes and plasma cells. Multifocally, within the superficial dermis, few macrophages contain melanin granules (pigmentary incontinence). There is minimal hyperplasia and hyperkeratosis of follicular epithelium. Diffusely, the epidermis is mildly hyperplastic with short rete ridges.
MORPHOLOGIC DIAGNOSIS: Haired skin, dermis: Mucinosis, diffuse, moderate, with minimal, chronic-active dermatitis, Chinese shar-pei, canine.
CONDITION: Cutaneous mucinosis
SYNONYMS: Idiopathic mucinosis, congenital myxedema
- Chinese shar-peis have greater amounts of dermal mucin than other dog breeds and some degree of diffuse mucinosis in this breed is considered normal; however clinically relevant generalized mucinosis can occur and is most common in this breed
- Association between the shar-pei breed and genetic variation in hyaluronic acid synthase 2 (HAS2) has been demonstrated
- Mucin, a jelly-like, clear, viscous glycosaminoglycan composed of hyaluronic acid bound to heparin and chondroitin sulfate B, is produced in the skin by dermal fibroblasts and is a component of the normal dermal ground substance; also found in superficial and follicular epidermis
- Hyaluronic acid, a nonsulfated carboxylated glycosaminoglycan, is the most common glycosaminoglycan in canine mucinosis; sulfated carboxylated glycosaminoglycan such as chrondroitin 4-sulfate, chrondroitin 6-sulfate, and dermatan sulfate may also be found in mucinosis; its production decreases with age
- Mucinosis may be divided into two categories:
- Primary mucinosis can be divided into hereditary (generalized or multifocal), papular, nodular, and myxedema forms
- Secondary mucinosis is usually a clinically silent finding detected histologically, and is associated with inflammatory skin conditions such as pyoderma, allergic skin disease, eosinophilic skin disease, and lupus erythematosus, as well as neoplastic diseases such as mast cell tumors
- Generalized primary hereditary mucinosis involves no compromise of normal skin integrity; multifocal hereditary mucinosis is often accompanied by some generalized mucinosis, but may result in multifocal compromise of skin integrit
- Myxedema is a rare manifestation of canine hypothyroidism; it results in symmetrical thickening of skin in the face to give the classic ‘tragic faces’ appearance
- Mechanism of deposition in cutaneous mucinosis is unknown
- Certain mast cell subtypes are believed to have a role in the pathogenesis for clinically relevant disease in Chinese shar-peis
TYPICAL GROSS FINDINGS:
- Exaggerated thickening and folding of spongy skin most pronounced on the head, ventrum, and the distal extremities
- In multifocal disease, variably sized mucinous vesicles, occurring in normal or edematous skin that when expressed discharge a thick, clear and sticky fluid
- If severe, skin integrity may be compromised and abraded areas may exude mucin
- Snoring and snorting because of involvement of swollen oropharyngeal mucosa
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- The primary lesion is dermal thickening due to increased accumulation of pale-staining, blue-purple, fibrillar to granular mucin strands arranged in a lacy network and separating dermal collagen bundles in the superficial and deep dermis
- Clear spaces represent fluid removed during processing because of the hygroscopic nature of the glycosaminoglycan
- Focal mucinosis is characterized by lakes of mucin in the superficial and middle dermis that displace normal dermal collagen
- Epidermis is usually normal in uncomplicated cases; however, most shar-peis have concurrent inflammatory skin disease (pyoderma or demodicosis)
- Amorphous granular material dilating the cisternae of dermal fibroblasts and aggregating in the interstitium
ADDITIONAL DIAGNOSTIC TESTS:
- Alcian blue will stain mucin blue or blue-green
- Periodic-acid Schiff is negative because of the acid mucopolysaccharide nature of the increased dermal mucin
- Elevated serum HA concentration
- Myxedema is used specifically to indicate the mucinosis seen with canine hypothyroidism and presents as a symmetrical thickening of facial skin that imparts the classic ‘tragic faces’ appearance
- Serum HA concentration is normal
- Papular mucinosis presents as solitary or occasionally multiple, white or yellow papules or clear “blisters” noted as incidental findings and most frequently localized to the head and neck
- Urticaria may be a primary differential histologically if there is high water content in the mucin; mucin stains can be used to differentiate
- Relatively common in Chinese shar-pei
- Rare in other breeds
- Very rare in the cat
- Similar condition reported in Brown-egg laying chickens, although combs and wattles which generally have a large amount of mucin in the dermis, were not affected
- Gross TL, Ihrke PJ, Walder EJ, Affolter VK. Skin Diseases of the Dog and Cat, Clinical and Histopathologic Diagnosis. 2nd ed. Ames Iowa: Blackwell Publishing; 2005:380-383.
- Mauldin EA, Peters-Kennedy J. Integumentary system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 6th ed. Edinburgh, England: Elsevier; 2016:522-523.
- Momoto Y, Yamamoto M, Yoshimastu H, Satoshi N, Shigihara K, Yasuda A, Hayakawa N, Ikezawa M, Tani, K, Mori A, Sako T. Nodular cutaneous mucinosis in a hypothyroid dog- a severe form of myxedema. Vet Derm. 2016; 27:61-63.
- Palmieri C, Anthenill L, Sjivaprasad HL. Cutaneous mucinosis in a strain of brown-egg laying chickens. Vet Pathol.2015;52(2):351-355.
- Scott DW, Miller WH, Griffin CE. Muller and Kirk’s Small Animal Dermatology. 6th ed., Philadelphia, PA: W.B Saunders; 2001:996-997.