Thyroid

Hypothyroidism

Symptoms

• Weakness
• Fatigue
• Memory impairment
• Cold intolerance
• Constipation
• Loss of hair
• Hoarseness
• Deafness
• Menstrual irregularity

Signs

• Dry coarse skin
• Periorbital edema
• Coarse thin skin
• Thick tongue
• Slow speech
• Deep voice
• Delayed  Achilles' tendon reflex time
• Bradycardia

Primary hypothyroidism

• Hashimotto's thyroiditis / Family history or the presence in the patient of other autoimmune endocrine disease
  • Schmidt's syndrome / Hashimotto's and Pernicious anemia and Diabetes Mellitus
• Idiopathic
• Post therapy for hyperthyroidism
  • Radioactive iodine therapy / History of radioactive iodine therapy
  • Subtotal thyroidectomy / History of thyroidectomy
• External beam radiotherapy /  history of neck radiation for lymphoma or head and neck cancer
• Lithium, Amiodarone
• Iodide deficiency / underdeveloped countries

Secondary hypothyroidism

• Hypothalamic dysfunction / symptoms of hypothalamic disease such as diabetes insipidus, narcolepsy, excessive appetite or marked anorexia, hyperthermia or marked hypothermia.
  • Therapeutic irradiation
  • Hypothalamic tumor (germinoma, meningioma, hamartoma)
• Pituitary dysfunction /secondary adrenal insufficiency , hypogonadism, growth hormone deficiency
  • Pituitary tumor / a space-occupying mass such as headache, bitemporal hemianopsia, 3rd, 4th, or 6th nerve defects, seizures, rhinorrhea, meningitis
  • Post partum Pituitary necrosis / history of shock or massive hemorrhage at time of delivery as well as inability to breast feed and amenorrhea afterwards
  • Sarcoidosis / symptoms of systemic illness 
  • Metastatic carcinoma involving pituitary, hypothalamus or stalk 
  • Rathke's cleft cyst, craniopharyngioma, carotid artery aneurysm compressing pituitary

Tests that would help confirm the diagnosis of hypothyroidism

• Total T4:  Low
• Free T4: Low
• Free T3:  of no value
• TSH
  • Increased / Primary
  • Decreased / secondary
• TRH stimulation: Primary / Exaggerated TSH response
• Thyroid autoantibodies are insensitive
• Diagnostic tests for secondary Hypothyroidism / Pituitary / Hypothalamic dysfunction

Tests helpful in the diagnosis of secondary hypothyroidism

• MRI with gadolinium enhancement to document the presence of a mass
• Baseline and dynamic anterior pituitary hormone testing for deficiencies and overproduction
• Testing for other tumor markers (alpha subunits)

Non specific lab abnormalities of hypothyroidism

• CPK
• Anemia
• Bradycardia, low voltage and non specific ST T wave changes
• Hypoxia with hypercapnea

Treatment options for primary hypothyroidism

• Thyroid hormone replacement therapy with non-generic l-thyroxin or a generic form that has undergone rigorous quality controlled supervision of the manufacturing process. 
• With risk factors for coronary arterial disease, it would be wise to start with a low dose of thyroid hormone and raise the dose slowly.

Treatment options for secondary hypothyroidism

• Evaluate if secondary hypoadrenalism is present. 
• If present treat simultaneously with the treatment of the hypothyroidism. 
• Also evaluate whether hypogonadism and/or growth hormone deficiency is present and treat accordingly.
• Then treat the cause of the secondary hypothyroidism. 

Components of Total serum throxine

• Free thyroxine 0.03%
• Thyroxine binding albumin 10%
• Thyroxine binding prealbumin 20%
• Thyroxine binding globulin 70%

Alterations in these binding proteins can alter serum thyroxine values and mistaken diagnosis of hypo or hyperthroism can be made.

Euthyroid  hypothyroxinemia / sick syndrome

• Clinical picture
• Normal sized thyroid gland
• Low serum TBG
• Hypoalbuminemia / Nephrotic syndrome, Cirrhosis
• Low serum total T4
• Normal free T4
• Normal TSH
• TSH response to TRH normal

Subclinical hypothyroidism

• Euthyroid
• Normal serum T4 and T3
• Elevated TSH

Hyperthyroidism

Symptoms: Potentiation of sympathetic system by excess Thyroxine

• Nervousness

• Heat intolerance

• Palpitations

• Tremor:

• Weight loss inspite of voracious appetite

• Weakness particularly proximal muscle group

• Hyper defecation

Signs:

• Thyroid enlargement

  • Pyramidal lobe

  • Brui

• Potentiation of sympathetic system by excess Thyroxine

  • Lid lag

  • Warm moist skin

  • Fine tremor

  • Brisk reflexes

  • Tachycardia

• Onycholysis / Plummer's nails

• Mucopoysaccharide infiltration

  • Proptosis

  • Ophthalmopathy: Diplopia

  • Pretibial myxedema 

  • Clubbing/ Thyroid acropachy

Etiology

• Graves disease

• Toxic multinodular goiter

• Toxic adenoma

• Factitious thyrotoxicosis

• Toxic struma ovari

• Thyroiditis

Tests

• Total T4:  high
• Free T4: High
• Free T3:  High
• TSH: Decreased
• TRH stimulation : Flat TSH response 
• RAIU/ Scintiscan
  • Increased / Graves
  • Heterogynous / Thyroiditis, Multinodular goiter
  • Hot nodule / Toxic adenoma
  • Decreased / Factitious and struma ovari and Thyroiditis
• TRAb
• TSI
• Sonography: Serial size of thyroid nodule on T4 suppressive therapy

Euthyroid hyperthyroxinemia (alterations in TBG)

• High serum TBG
• Estrogens, Hepatitis, 5-fluorouracil
• High serum total T4
• Normal free T4
• Normal TSH

Euthyroid hyperthyroxinemia (unrelated to TBG)

• Clinical picture
• Normal sized thyroid gland
• High serum total T4
• High free T4
• Acute non-thyroidal illness, Psychiatric illness, drugs

• Antithyroid drug therapy
• Radioactive iodine therapy
• Surgery
• Symptomatic therapy with beta blockers

Treatment options based on etiology

• Graves disease
• Toxic  multinodular goiter
• Toxic adenoma
• Thyroiditis / Symptomatic therapy only
• Factitious Thyrotoxicosis / Treat the personality problem