Hypothyroidism

Internal Medicine

HYPOTHYROIDISM (underactive gland)

Feature	Primary	Secondary
Location of Problem	Thyroid gland	TSH secretion from brain (very rare)
T3/T4 levels	Low	Low
TSH levels	High	Low (main problem)

PRIMARY HYPOTHYROIDISM

ETIOLOGIES

1. Hashimoto thyroiditis ( most common cause)
2. Iodine deficiency
3. Surgical gland removal
4. Radio-iodine therapy for hyperthyroidism (gland destruction)
5. Radiotherapy to the neck region
6. Hypothyroidism induced Drugs (Interferon, amiodarone)

S/S of hypothyroidism

1. Weight gain
2. Tiredness/ fatigue
3. Cold intolerance
4. Constipation
5. Dry skin, dry hair
6. Hair fall
7. Bradycardia
8. Hyporeflexia
9. Menstrual irregularities
10. Infertility ( rule out hypothy. in any female with 9 or 10)
11. Increased sleep
12. Slowed actions
13. Dementia, mental slowness, psychosis
14. Puffy eyes
15. Myalgias, arthralgias
16. *Carpal tunnel syndrome *

WHAT IS MYXEDEMA

Hypothyroidism plus generalised edema due to deposition of subcutaneous mucopolysaccharides. Leads to thickening of facial features & generalised edema

All hypothyroid patients do not have myxedema

MYXEDEMA COMA

Investigations in hypothy.

1) TFTs:

• Low fT4 & fT3
• High TSH ( low in sec. hypo)

2) In Hashimoto’s thyroiditis: Serum anti TPO ab. very high

3) CBC: Usually macrocytic anemia, but may be microcytic

4) Hyponatremia

5) High CPK

6) High cholesterol & triglycerides

7) Radio I scan shows decreased uptake (but not done as a routine)

TREATMENT of HYPOTHYR.

• Levothyroxine tabs. (synthetic T4) is the main treatment
• Taken for ever
• Take in an empty stomach
• Start with a medium dose about 50 micrograms/d in young & otherwise healthy people. Increase as neededRR
• In elderly & in IHD, start 25 mcg (higher dose can cause arrhythmias)
• Levothyroxine is safe in preg. & should be continued RR
• Check TFTs 6 weeks after starting or any dose change (TSH takes some to normalise)
• Increase the dose gradually ( about 25mcg). Rapid hormone correction is dangerous (arrhythmias)
• Once TSH, T3 & T4 are normalised, maintain the dose. Later, routine TFTs once a year is enough
• Do not suppress the TSH to below normal - Improvement of S/S takes a few months

---

MED & SURGERY

• Primary:
  • Hashimoto’s disease
  • Post RAI for Grave’s disease
  • Post thyroidectomy
  • Sub-acute thyroiditis
  • Iodine deficiency
  • Goitrogens use- lithium, anti-thyroid drugs
  • Inborn errors of thyroid hormone synthesis
• Secondary:
  • Hypopituitarism

SIGNS OF HYPOTHYROIDISM

• Obese
• Dry inelastic skin
• Macroglossia
• Mask like facies
• Loss of hair in lateral eyebrow
• Hoarseness of voice
• Pseudomyotonic reflex (delayed ankle jerk); also called ‘hung up’ reflex

---

---

Thera

Defined as low free T4 level with a normal or high TSH.

Causes of hypothyroidism:

A- Primary: Thyroid gland dysfunction Most common:

1. Congenital hypothyroidism (in neonates) = Cretinism
2. Chronic lymphocytic thyroiditis (Hashimoto`s thyroiditis) Autoimmune disease of thyroid. Thyroid gland is enlarged
3. Iodine deficiency +++
4. Thyroid surgery (total thyroidectomy)
5. Radioactive iodine treatment

B- Secondary: Pituitary hypofunction          (hypopitutarism due to radiation therapy or destruction of the pituitary)

Laboratory Investigation:

1. Low plasma free T4…..
2. Plasma TSH is normal or high in 1ry hypothyroidism &
3. low in 2ry hypothyroidism
4. Neonatal screening for congenital hypothyroidism = Cretinism (plasma TSH is elevated in affected neonates)

clinical manifestations of hypothyroidism:

Symptoms:

• Cold intolerance
• Depression
• Mental retardation (infants)
• Growth failure (children)
• Dry skin
• Constipation
• Dyspnea on exertion

Signs:

• Bradycardia
• Periorbital edema
• Slowed movement & speech
• Delayed relaxation phase of deep tendon reflex tendons
• Lab: Hypercholesterolemia