Dermatology and Endocrine Diseases

Question 1

What are your dermatologic differential diagnoses?

Answer 1

• Parasitic: fleas, scabies, demodex, other
• Allergic: environ, food, parasite, contact
• Immune mediated/Idiopathic
• Neoplastic
• 4: 1-4 other misc (refer to someone else)
• Microbial: bacteria, yeast, dermatophyte
• Endocrine: endogenous

Question 2

What are 3 endocrine dermatopathies?

Answer 2

• hypothyroidism (dogs)
• Cushing’s dz (dogs, cats, horses)
• Alopecia X (dogs)

Question 3

What are general concepts regarding endocrine dermatopathies?

Answer 3

• usually middle aged animals
• alteration in hair coat (alopecia, texture)
• underlying non-pruritic dz, responsible for recurrent skin and ear infections

Question 4

What is the different between T₃ and T₄?

Answer 4

• T₃ = more metabolically active
  
  • mainly intracellular
  • only 10-20% produced directly by thyroid, most from deiodination of T₄
• T₄ = most often on measured clinically
  
  • main thyroid secretory product that is tested, but not as biologically active

Question 5

What are the functions of thyroid hormones?

Answer 5

• growth
• protein synthesis
• lipid metabolism
• carb metabolism
• hematopoiesis
• reproduction

Question 6

What occurs if a patient has low thyroid hormone?

Answer 6

• Growth: alopecia
• Protein synthesis: altered metabolism
• Lipid metabolism: elevated cholesterol
• Carb metabolism: alteration
• Hematopoiesis: anemia (mild)
• Reproduction: decreased

Question 7

What are the general (non-derm) clinical signs of hypothyroidism?

Answer 7

• Metabolic: lethargy ,inactivity, wt gain, cold intolerance
• Reproductive: persistent anestrus, testicular atrophy
• CV: bradycardia, cardiac arrhythmias
• GI: diarrhea, constipation
• Hematologic: anemia, hyperlipidemia
• Neuromuscular: seizures, ataxia, circling, vestibular signs, facial n. paralysis
• Ocular: corneal lipid deposits, uveitis

Question 8

What are the dermatologic clinical signs of hypothyroidism?

Answer 8

• seborrhea: dry or greasy
  
  • skin and/or ears
  • may not be affected
• recurrent infections: skin and/or ears
• hyperpigmentation
• dry, brittle hair coat
• alopecia: variable
• different patients, different constellations of symptoms

Question 9

What are the breed predilections for hypothyroidism?

Answer 9

• Golden retrievers
• Dobies
• Dachshund
• Great Dane
• Poodle
• Boxer

Question 10

How do you diagnose hypothyroidism?

Answer 10

• CBC: normochromic, normocytic, non-regenerative anemia
• Chem: incr cholesterol and triglycerides
• Thyroid panel:
  
  • decr TT4, FT4 = decr T4 (most common)
  • TSH (incr primary hypothyroidism, but decr in secondary and tertiary hypothyroidism)
  • TT3 and FT3 unreliable

Question 11

What are some factors that affect thyroid hormone synthesis?

Answer 11

• age
• breed
• drugs
• illness (euthyroid syndrome)
• hypoproteinemia
• obesity

Question 12

What are the advantages of FT₄ over TT₄?

Answer 12

• direct correlation w/ availability to tissues, rate of metabolism and excretion
• less influenced by medical conditions and drug competition
• most labs offer “inexpensive” T4

Question 13

What changes on a skin biopsy might be suggestive of endocrine disease?

Answer 13

• hyperkeratosis and follicular keratosis
• incr in telogen hair follicles

Question 14

How do you treat hypothyroidism?

Answer 14

• synthetic T4 supplementation (L-thyroxine)
• monitor: post pill check 6 hrs after dose, 6 wks after beginning treatment

Question 15

What are some reasons for therapeutic failure for hypothyroidism?

Answer 15

• wrong diagnosis, dose, product, frequency
• irregular admin
• failure to ingest the medication
• poor absorption from the gut
• rapid metabolism/excretion
• auto-antibodies to T3 or T4
• target organ resistance

Question 16

What are the clinical signs of Cushing’s disease?

Answer 16

• PU/PD/PP
• Incr panting
• Pendulous abdomen
• Hepatomegaly
• Lethargy
• Mm weakness
• Mm atrophy
• obesity
• anestrus
• testicular atrophy
• facial n. palsy
• skin dz: sometimes only symptom

* hypothyroidism C/S also

Question 17

What are the dermatologic clinical signs of Cushing’s?

Answer 17

• alopecia
• comedones (+/- Demodex)
• recurrent infections
• Demodicosis (+/- comedones)
• Cutaneous atrophy
• Hyperpigmentation
• Calcinosis cutis

* same C/S as hypothyrodism

Question 18

What are the tests you can run to diagnose Cushing’s disease?

Answer 18

• ACTH stim test
• Low dose dex suppression*
• High dose dex suppression*
• Imaging

* since steroids interefere with thyroid testing, r/o Cushing’s before considering hypothyroidism

Question 19

What are the clinical manifestations of Cushing’s disease in cats?

Answer 19

• Diabetes mellitus
• skin fragility
• calcinosis cutis - iatrogenic (rare)

Question 20

Describe Alopecia X

Answer 20

• ​also called:
  
  • adrenal sex hormone imbalance
  • growth hormone responsive dermatosis
  • PseudoCushing’s
  • Castration responsive dermatosis
• pathogenesis not established
• breed predilection:
  
  • Pomeranians, mini poodles, Chows, Samoyeds

Question 21

What are the clinical signs of adrenal sex hormone imbalance/alopecia x?

Answer 21

• bilaterally symmetrical alopecia
• head and extremeties are spared
• hyperpigmentation
• no systemic abnormalities

Question 22

How do you diagnose Alopecia X?

Answer 22

• r/o hypothyroidism and Cushing’s dz
• ACTH stim test and sex hormone levels
  
  • UTennessee
  • progesterone levels often evaluated

Question 23

How do you treat Alopecia X?

Answer 23

• not necessary
• melatonin
• if dog is intact, castration is rx
• if dog is neutered, methyltestosterone
• Ketoconazole
• Lysodren: monitor ACTH response
• Trilostane

Question 24

What are the dermatologic signs of Sertoli cell tumors?

Answer 24

• bilateral symmetrical alopecia
• hyperpigmentation
• seborrhea
• ceruminous otitis externa
• gynecomastia
• linear preputial dermatosis