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Case Report
Chow, male (entire), 6 years old, 23kg.
Owner’s complaint – hair loss with some itching.
History • 15 month history of multifocal hair loss and mild pruritus.
• Low T4, low T3, low FT4, normal TSH.
• Hypothyroidism diagnosed but no improvement with sid Soloxine.
Clinical examination –
• Multifocal hair loss – neck, trunk, tail, caudal thighs.
• Affected skin hyperpigmented with scale, papules,
occasional pustules and comedones.
Differentials - scabies, demodicosis, atopy, food intolerance, flea allergy,
intestinal parasite hypersensitivity, pyoderma, malassezia overgrowth,
ringworm, sebaceous adenitis, endocrine disease.
Laboratory investigations •
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Cytology – malassezia yeasts negative.
Skin scrapings - negative.
Haematology and biochemistry panels – NAD.
Scabies serology - positive.
IgE aeroallergen serology -negative.
Dermatophyte culture - negative.
Bacterial culture – Staph. pseudintermedius.
Faecal parasite screening – negative.
Histopathology – atrophic dermatopathy with superficial pustular
dermatitis consistent with endocrine disease +/- pyoderma +/ectoparasitism.
Provisional diagnosis • Scabies.
• Pyoderma.
• Endocrine disease.
Pruritus persisted despite Stronghold – scabies unlikely despite positive
serology.
Pruritus resolved with antibiosis – supporting a diagnosis of pyoderma.
Pyoderma is a common complication of other underlying dermatological
disease, including endocrinopathies.
Differential diagnosis of endocrine alopecia – hypothyroidism,
Cushing’s disease, sertoli cell tumour, castration responsive dermatosis,
adrenal dysregulation, GH responsive dermatosis, alopecia X.
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Further investigations –
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ACTH stimulation test – cortisol and 17-OH-progesterone – normal.
Dexamethasone suppression test – normal.
Normal serum oestradiol and testicular ultrasound.
IGF1 – normal.
T4 7.3 nmol/l (13-52) – reduced.
TSH <0.10 ng/ml (<0.41) – normal.
A tentative diagnosis of hypothyroidism (with secondary pyoderma) was
made. Historically the dog had failed to respond to oral T4
supplementation sid.
Oral Soloxine 0.3mg bid was prescribed and after 2 months no
improvement was observed despite adequate serum T4 levels.
T4 6 hours post pill 55nmol/l (13-52)
T4 12 hours post pill 47nmol/l (13-52)
Some unexplained canine alopecia cases will respond to castration –
castration responsive dermatosis. The dog was castrated and no gross or
histological testicular abnormalities were noted.
Three months later there was no hair growth and the owner reported
lethargy.
Serum T4 levels remained low –
T4 9.8nmol/l (13-52)
T3 0.3nmol/l (0.3-2.5)
The dog was prescribed oral Tertroxin 100ug tid with an almost immediate
attitudinal response and complete regrowth of hair within 3 months.
Over a 5 year follow up there was no recurrence of the alopecia with
ongoing T3 supplementation. There were occasional pyoderma relapses
that responded to appropriate antibiosis.
Final diagnosis – hypothyroidism with secondary pyoderma.
Discussion –
Hypothyroidism is a well recognised but over diagnosed endocrinopathy in the dog. Definitive diagnosis can be
difficult. Some breeds and individuals have low serum T4 levels, and euthyroid sick syndrome is a confusing
complication.
Clinical signs include hair loss and lethargy. Pyoderma, often pruritic, is a not uncommon complication and can
be an ongoing issue even with adequate thyroidal supplementation. Most dogs do well on oral T4.
Treatment failures are usually associated with inadequate T4 dose or poor owner compliance. Neither was an
issue in this case.
It is very unusual to see T4 resistant but T3 responsive hypothyroidism in the dog. Oral T4 is the preferred
treatment in most animals requiring only sid or bid dosing, as opposed to tid dosing with T3, and is advantageous
on cost grounds and the availability of veterinary licensed formulations.
One can postulate in this case that, although intestinal absorption was adequate, there may have been a
conversion problem at tissue level from T4 to the more metabolically active T3.
Chris Dale MA VetMB CertSAD MRCVS
Chris Dale will be holding regular Dermatology clinics at Beechwood Veterinary Hospital. To refer or
discuss a case please contact 01302 534999 or email [email protected].
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