Exam 2: Disorders of Hair Follicles & Pigmentation

Question 1

What are the mechanisms of alopecia?

Answer 1

Follicular dysplasia (abnormal formation)
Follicular atrophy (genetic, ischemic, trauma, inflammation)
Abnormal growth/hair cycle arrest (endocrine, nutritional, metabolic)

Question 2

What are the clinical lesions of endocrine alopecia?

Answer 2

Non-pruritic, bilaterally symmetric alopecia
Remaining hair coat = dull, dry, easily epilated, fails to regrow after clipping

Question 3

What are the histological lesions of alopecia?

Answer 3

Hair follicles = catagen or telogen phase with lack of hair shafts
Epidermis = normal, atrophic, or hyperplastic

Question 4

What are the limitations of histologic diagnosis of alopecia?

Answer 4

Histopath suggests endocrine alopecia, but clinical testing/clinical signs needed to differentiate various disorders

Question 5

What lesions are associated with hypothyroidism?

Answer 5

Generalized truncal alopecia

Question 6

What lesions are associated with hyperadrenocorticism?

Answer 6

Calcinosis cutis (dogs) = dystrophic mineralization
Fragile skin (cats)

Question 7

What lesions are associated with hyperestrogenism?

Answer 7

Alopecia

Question 8

What lesions are associated with hyposomatotropism (pituitary dwarfism)?

Answer 8

Failure to grow and retention of puppy hair coat

Question 9

What lesions are associated with alopecia x?

Answer 9

Alopecia sparing head and distal extremities

Question 10

What are the (3) inherited mechanisms of depigmentation/hypopigmentation and what causes them?

Answer 10

Peibaldism: genetic absence/failure of migration of melanocytes to regions
Albinism: melanocytes present, but defective in function/synthesis of melanin
Vitiligo: destruction of melanocytes

Question 11

What are the acquired mechanisms of depigmentation/hypopigmentation?

Answer 11

Destruction of the epidermal-melanocyte units
Reduced melanin synthesis (tyrosinase, Cu deficiency)

Question 12

What is an example of acquired hypopigmentation associated with destruction of the epidermal-melanocyte units?

Answer 12

Autoimmune (lupus, uveodermatologic syndrome), post-inflammatory disease, trauma, neoplasia

Question 13

What are the mechanisms of hyperpigmentation?

Answer 13

Acquired (e.g. chronic inflammation/irritation, UV exposure) = increased proliferation of melanocytes, increased rate of melanin synthesis
Lentigo = non-neoplastic proliferation of melanocytes