Disorders of Thyroid and skin.

Hormones are produced in body by different glands for the regulation of vital body functions.When there is a disturbance of there production in body one can expect hormonal diseases manifested by different clinal symptoms and one of them could be in the form of skin disease. It means skin affection is one of the several symptoms and so skin diseases due to hormonal disturbances are difficult to diagnose .

The Thyroid ,Adrenal ,Pituitary, Testical,and Ovary are the main glands which produce harmones and when production deficient (hypo) and when excessive ( hyper) there are visible changes in the skin of the pet.

Disorders of Thyroid and skin.

Skin changes are associated with both deficiencies and excess of thyroid hormone.
The thyroid gland lies on the trachea, just below the larynx; triiodothyronine and levothyroxine, the hormones produced by the thyroid, govern the body's basic metabolism including control of growth and development and maintenance of protein, carbohydrate, and lipid metabolism throughout life. Failure of the thyroid gland means trouble of one sort or another for the body.

Skin changes are associated with both deficiencies and excesses of Thyroid hormones.
In the hypothyroid state ,several event occur.
Anagen fails to be initiated ,and hair follicles enter telogen ,the resting stage.There is abnormal hair shedding and poor or absent regrowth. Epidermal keratinization becomes disordered leading to scaling ,thickening.
Sebaceous glands atrophy leads to decreased secreation.There is accumulation of abnormal irritating ceruminous secretions in ears can cause Otitis externa.
Hyperpigmentation often occurs mechanism is unknown.
Myxedema may devlop especially in chronic and severe hypothyroidism.
Skin is cool to touch. There is predispotion to pyodermas,malassezia,and demodicosis.Poor healing and increased bruising can occur.
The hyperthyroid state produce two basic changes. 1)Psychoactive effect results in lack of attention to grooming and / or hair pulling (cats )
2)Hypermetabolic state produces increased skin temperature and vasodilation ,which may be pruritogenic (cats ).

Clinical signs:
1.Hypothyroidism .
Cutaneous signs devlop slowly over a period of several months where the hairs are dull, dry, coarse, and brittle and may become discoloured ( black to reddish ).
Seborrhea sicca is evident where there is dry and scaly skin.
Seborrhea oleosa occasionally present where there is oily or greasy skin.
Alopecia is common. Poor or absent regrowth following clipping.Abnormal shedding patterns are there .Initially ,often patchy or asymmetrical ,primarly affecting the area or normal wear e.g dorsum of tail,which may become more bilaterally symmetrical and truncul but spares the head and distal extremities.The udercat is lost giving the coarse appeareance to the coat.
Hyperpigmentation is first noticed in alopecic areas and then beome generalized and symmetrical.
Myxedema is seen as thickening of and folding of the skinand is most common over the head giving the pet a tragic expression and on the distal extremities.
Skin changes are non pruritic and when pruritus is present it is attributed to the secondry bacterial infections and severe seborrhea.
In congenital initially there is retention of puppy coat and poor growth of primary hairs.

In cats coat and skin is generally dull ,dry ,and scaly .Pinnal alopecia is common. Symmetrical ,truncal alopecia is un common.

Feline Hypothyroidism
There is usually excessive sheding ,matting and scaling and a general unkept appearance.
Skin is warm and moist.Alopecia caused by self - trauma is most commonly noted over the caudal thighs ,inguinal regions ,back and sides.There is increased rate of nail growth.

Diagnosis
1. Routine lab tests .
CBC (normocytic normochromic anaemia in 25-30% ) .
2. Serum chemistry
Hyperchlorestelolemia (in 50 - 70%)
Elevated CK ( 10-50%)
Mild elevation in AP
3. Thyroid function test
Necessary to confirm hypothyroidism.
1. Normal canine T4 is 20-52 nmol /L (15-40 ng/ml)
2. Normal canine T3 is 1.2- 3.1 nmol/L (0.8-2ng/ml)
3. resting T4 concentration is more reliable .
Serum -free T3 and T4 concentration
1.Thyroid hormones are highly protein bound (>99 %)
Non protein bound or free t4 and t3 are the metabolically active fractions of thyroid hormones. Measurement of free T4 by equilibrium dialysis is superior to other assay methods because it is less affected by nonthyroidal illness and drug administration.

Serum canine thyroid stimulating hormones can also now be measured.
Elevated serum thyroid stimulating hormones and subnormal serum T4 are diagnostic of hypothyroidism in adog with typical clinical signs

Clinical signs with tests are generally used for the thyroid diseases in dogs.

Treatment and monitoring

1.Hypothyroid disorder
Adequate thyroid hormone supplementation should resolve the clinical manifestation.
First hair growth is seen withih 3-4 weeks .During the first 2-6 weeks of therapy excessive shedding, scaling and pruritus can result from reactivation of cutaeous metabolism so antiseborrheic shampoos and moisturizers with predisolone ,starting at 0.5-1mg/kg/day and decreasing over1-3 weeks.
Sodium levothyroxine (T4) is the hormone of choice at the dose of 0.5mg/m3 Po BID .Dosage interval may be reduced in most of the dogs to SID after resolution of clinical signs and can be increased again if reuccurence is there.
Cats - dose is 0.05-0.1 mg PO BID

Thyrotoxicosis is rare in dogs and cats as they rapidly metabolise thyroid hormones.

2. Hyperthyroidism .

Antithyroid drugs
Methimazole . Drug of choice at the dose rate of 5mg/cat PO SID to TID .

Institute grooming program .Usally 1-3 months time is required for the skin to improve.