Overview of the Issue

When a patient is nonpruritic, it can be difficult to determine the underlying etiology. Many diseases look strikingly similar and often a diagnosis can only be made after ruling out diseases on your differential list one at a time.

Objectives of the Presentation

Review diagnostic steps for the nonpruritic patient with skin disease.

Key Etiologic and Pathophysiologic Points

Hair loss can be both inflammatory and non-inflammatory. Inflammatory causes encompass parasitic disease, infectious disease, immune mediated disease and neoplasia. Non-inflammatory alopecia occurs when there is either hair cycle arrest or when abnormal hair is formed due to a dysplastic disease process. The etiology for many of these diseases is not well understood. Certain parasitic diseases (demodicosis) and fungal infections (dermatophytosis) are also often nonpruritic.¹

Hair Cycle Arrest Alopecia

1.  Endocrine disorders (hypothyroidism, hyperadrenocorticism)

a.  Require appropriate blood tests to diagnose

b.  Systemic signs may also be present

2.  Alopecia X2

a.  Hairs remain in telogen

b.  Possible abnormal adrenal sex hormone imbalance

c.  and growth hormone deficiency

d.  Possible local follicular receptor dysfunction

e.  Young dogs (2–5 y)

f.  Chow Chow, Samoyed, Pomeranian, Alaskan Malamute, Keeshond, Husky, Miniature Poodle

g.  Truncal alopecia starting around perineum and caudal thighs

h.  Head and neck spared

3.  Canine recurrent flank alopecia

a.  Alopecia of the flanks (thoracolumbar region), often recurrent between November and March each year

b.  Symmetrical or asymmetrical

c.  Hyperpigmentation

d.  Often will regrow within 3–8 months

e.  Due to changing photo period, pineal gland and prolactin secretion

f.  Boxer, Airedale Terrier, Bulldog

4.  Post clipping alopecia⁴

a.  Hair fails to regrow after clipping

b.  Chow Chow and Husky

c.  Regrowth after 3–4 months

Dysplastic Alopecia

1.  Congenital alopecia/hypotrichosis⁵

a.  Dogs and cats born without hair

b.  Ectodermal defect

2.  Colour dilution alopecia

a.  Alopecia associated with blue (dilute black) or fawn (dilute brown) coat colours

b.  Defective hair pigment results in the formation of large pigment granules

c.  Can fracture hair shafts leading to alopecia

d.  Doberman, Dachshund, Great Dane, Yorkshire Terrier, Whippet, Greyhound, Miniature Pinscher, Saluki, Chow Chow, Boston Terrier, Shetland Sheepdog, Chihuahua, Poodle and Irish Setter

e.  Normal at birth then hair loss occurs around 6 months

f.  Non colour dilute areas remain normal

3.  Black hair follicular dysplasia¹

a.  Familial in bicoloured/tricoloured dogs

b.  Only black hair affected—possible defect in pigment transfer

c.  Bearded Collie, Basset Hounds, Saluki, Beagle, Dachshund, Pointer

d.  Normal at birth then progressive loss of black hairs around 4 weeks

4.  Follicular dysplasia^1,7

a.  Abnormal hair follicle development

b.  Doberman Pinscher, Miniature Pinscher, Manchester Terrier

c.  Husky, Alaskan Malamute

d.  Irish Water Spaniel, Portuguese Water Dog

e.  Greyhounds

5.  Pattern alopecia¹

a.  Idiopathic hair cycle arrest—miniaturization of hair follicles

b.  Alopecia of affected areas, usually symmetrical

c.  Three syndromes

i.  Male dachshunds—alopecia of pinnae

ii.  American Water Spaniels and Portuguese Water Dogs—alopecia of ventral neck, caudomedial thighs and tail

iii.  Female Dachshunds, Chihuahua, Whippet, Greyhound—alopecia of the post auricular area, ventrum and caudomedial thighs

Certain immune mediated diseases will also present with non-pruritic alopecia such as sebaceous adenitis and alopecia areata. These conditions need skin biopsies to definitively diagnose and immune modulating/suppressive therapy to treat.

Key Clinical Diagnostic Points

1.  It is important to remember that any “non-pruritic disease” can become pruritic if a secondary bacterial or yeast dermatitis is present. Therefore it is imperative to perform cytology on any animal with skin disease to rule in/out these secondary infections and pursue appropriate treatment.

2.  Skin scrapings must also be performed as demodicosis can present in many different ways and is often a nonpruritic disease.

3.  Fungal culture should be considered, as dermatophytosis is also a nonpruritic disease.

4.  Full bloodwork should be performed in any animal with non-pruritic alopecia. Results may provide evidence of underlying etiology if endocrine.

5.  Further blood tests including thyroid tests and tests such as an ACTH stimulation test for hyperadrenocorticism are also warranted (especially if the animal has other systemic signs indicative of these diseases, e.g., lethargy and weight gain for hypothyroidism or polyuria, polydipsia, polyphagia, “pot-bellied” appearance for hyperadrenocorticism).

6.  Trichograms (hair plucks) will provide valuable information and a potential diagnosis and are easily obtained and read in house.

7.  Skin biopsies sent to a dermatohistopathologist can provide more information and a potential diagnosis.

Key Prognostic Points

Many diseases can look the same on histopathology and therefore histopathology findings need to be paired with other diagnostic tests for an accurate diagnosis.

Summary Including 5 KEY “Take Home” Points

1.  Many nonpruritic, alopecic diseases look similar clinically.

2.  Perform baseline diagnostics including cytology, skin scrapings and fungal culture in any nonpruritic patient.

3.  A trichogram is a simple test that can be performed in house and can provide information regarding the etiology of the disease.

4.  Any nonpruritic disease can become pruritic if a secondary infection is present.

5.  Skin biopsies sent for dermatohistopathology can also provide extra information and a diagnosis.

References

1.  Miller WH, Griffin CE, Campbell KL. Miscellaneous alopecias. In: Miller WH, Griffin CE, Campbell KL, eds. Muller and Kirk’s Small Animal Dermatology. 7th ed. St. Louis, MO: Elsevier Mosby; 2013:554–571.

2.  Frank LA, Hnilica KA, Oliver JW. Adrenal steroid hormone concentrations in dogs with hair cycle arrest alopecia (alopecia X) before and after treatment with melatonin and mitotane. Vet Dermatol. 2004;15:278–284.

3.  Cerundulo R. Telogen effluvium. In: Mecklenberg L, Linek M, Tobin DJ, eds. Hair Loss Disorders in Domestic Animals. Ames, IA: Wiley Blackwell; 2009:161–162.

4.  Diaz SF, Torres SMF, Dunstan RW, Lekcharoensuk C. An analysis of canine hair regrowth after clipping for a surgical procedure. Vet Dermatol. 2004;15:25–30.

5.  Mecklenburg L. An overview on congenital alopecia in domestic animals. Vet Dermatol. 2006;17:393–410.

6.  Kim JH, Kang KI, Sohn HJ, Woo GH, Jean YH, Hwang EK. Colour-dilution alopecia in dogs. J Vet Sci. 2005;6:259–261.

7.  Cerundulo R, Lloyd DH, McNeil PE, Evans H. An analysis of factors underlying hypotrichosis and alopecia in Irish water spaniels in the United Kingdom. Vet Dermatol. 2000;11:107–122.