Hypothyroidism

Definition

Classification

Causes

Primary Hypothyroidism

• Hashimoto thyroiditis - the most common cause in the US and developed world. Antithyroid antibodies (especially TPO antibodies and thyroglobulin antibodies) attack thyroidal stroma, causing progressive fibrosis and declining T4 production. Female-to-male ratio 10-14:1, typically diagnosed in the fifth decade.

• Surgical ablation (thyroidectomy)
• Radioactive iodine (¹³¹I) therapy
• External radiation to head/neck

• Lithium (inhibits thyroid hormone release)
• Iodides (Wolff-Chaikoff effect)
• Amiodarone

• Thyroid dysgenesis (genetic defects in thyroid development)
• Dyshormonogenetic goiter (enzyme defects in hormone synthesis, e.g., deficient peroxidase, deficient iodide-trapping, deficient coupling)

• Riedel thyroiditis (IgG4-related disease; fibrosis of thyroid and surrounding structures; ~1/3 of patients develop hypothyroidism)

• Postpartum, sporadic, or subacute thyroiditis can cause transient hypothyroidism lasting 3-6 months

Secondary (Central) Hypothyroidism

• Pituitary failure - deficient TSH production
• Hypothalamic failure - deficient TRH production
• Suggested when TSH is low/normal with low FT4, without symptoms of thyrotoxicosis

Pathophysiology

1. Thyroid gland fails to produce adequate T4/T3
2. Loss of negative feedback on the pituitary/hypothalamus
3. TSH rises (in primary hypothyroidism)
4. Thyroid cells may be stimulated to grow (goiter), but without adequate substrate (iodine) or enzymes, hormone synthesis still fails
5. End result: decreased metabolic rate across all organ systems

Clinical Features

Congenital Hypothyroidism (Cretinism)

• Impaired skeletal and CNS development
• Severe irreversible intellectual disability (especially if maternal hypothyroidism occurs early in pregnancy, before fetal thyroid develops)
• Short stature, coarse facial features, protruding tongue, umbilical hernia
• Prevention: universal neonatal screening + iodine supplementation

Adult Hypothyroidism (Myxedema)

• Fatigue, lethargy, cold intolerance, weight gain
• Decreased sweating
• Generalized puffiness (myxedema - non-pitting edema from glycosaminoglycan deposition)

• Bradycardia, reduced cardiac output
• Diastolic hypertension
• Pericardial effusion
• Hypercholesterolemia (increased cardiovascular risk)

• Mental sluggishness, cognitive impairment
• Depression (may mimic primary psychiatric illness)
• Slow reflexes (prolonged relaxation phase)
• Peripheral neuropathy, carpal tunnel syndrome

• Cool, pale, dry, rough skin
• Hair loss, brittle hair
• Puffy face and periorbital edema
• Eyebrow thinning (lateral third - "Queen Anne's sign")
• Macroglossia

• Constipation (reduced GI motility)

• Menorrhagia, anovulation, infertility
• Galactorrhea (TRH stimulates prolactin)

• Muscle weakness, cramps, myalgia

Myxedema Coma (Severe/Emergency)

• Altered mental status / coma
• Hypothermia
• Bradycardia, hypotension
• Hyponatremia, hypoglycemia, hypercapnia

• IV levothyroxine (200-400 mcg loading dose) ± IV T3
• IV hydrocortisone (concurrent adrenal insufficiency must be treated)
• Supportive care (passive warming, airway management, fluid resuscitation)

Diagnosis

• Overt hypothyroidism: elevated TSH + low FT4
• Subclinical hypothyroidism: elevated TSH (typically 4.5-10 mIU/L) + normal FT4
• Central hypothyroidism: low/normal TSH + low FT4 - requires pituitary evaluation

Treatment

Levothyroxine (L-Thyroxine, T4) - First-Line

• Standard adult replacement dose: 1.6 mcg/kg/day
• Young, healthy adults: Can start at full replacement dose
• Elderly patients or those with cardiac disease: Start low (25-50 mcg/day) and titrate slowly to avoid precipitating angina or arrhythmia
• Monitoring: Serum TSH checked annually once stable; target TSH 0.5-2.5 mIU/L
• Taken on empty stomach, 30-60 min before breakfast; separate from calcium, iron, PPIs

Combination T4/T3 Therapy

• Considered in patients who remain symptomatic despite TSH in therapeutic range
• True T4-resistance is controversial
• If used, maintain TSH >1.0 mIU/L to avoid iatrogenic hyperthyroidism
• Not routinely recommended as first-line

Transient Hypothyroidism (e.g., post-thyroiditis)

• Usually resolves in 3-6 months
• Low-dose T4 may be used temporarily in symptomatic patients

Special Situations

• Pregnancy: Hypothyroidism must be aggressively treated; maternal hypothyroidism in early pregnancy (before fetal thyroid development) can cause irreversible fetal brain injury; TSH target <2.5 mIU/L in first trimester
• Subclinical hypothyroidism: Treat if TSH >10 mIU/L, symptomatic, or pregnant; individualize if TSH 4.5-10 mIU/L

Subclinical Hypothyroidism

• TSH mildly elevated (4.5-10 mIU/L), FT4 normal
• Affects 4-10% of the general population; 5-8% in pregnancy
• May be asymptomatic or have subtle symptoms
• Progression to overt hypothyroidism: ~2-4% per year (higher if TPO antibodies positive)

Key Associations

Mango Contact Dermatitis (Allergic Contact Dermatitis)

What You're Seeing in the Image

Why Mango Causes This

1. First exposure to urushiol (or cross-sensitization from prior poison ivy/oak contact) - sensitization phase - skin proteins bind to the resin, forming a novel antigen
2. On re-exposure (in your case, mango sap during harvesting) - T-lymphocytes mount a delayed immune response (Type IV, cell-mediated)
3. Symptoms appear 8-48 hours after contact, peaking at 2-5 days - which is why the connection to mango harvesting may not be immediately obvious

"Mango dermatitis is uncommon in natives of mango-growing countries who have never been exposed to Toxicodendron species. Many persons who have been so exposed are sensitized by one or a few episodes of contact with the peel of the mango fruit." - Andrews' Diseases of the Skin

Clinical Features (Typical)

Treatment

• Topical corticosteroid cream (e.g., hydrocortisone 1% OTC, or mometasone/betamethasone by prescription) - apply 1-2x daily to affected area for 1-2 weeks
• Oral antihistamine (e.g., cetirizine 10 mg once daily or chlorpheniramine 4 mg) - relieves itching
• Calamine lotion - soothing, drying agent, safe to use as needed
• Keep area clean and dry - avoid scratching to prevent secondary bacterial infection

• Oral prednisolone 40-60 mg/day, tapered over 3 weeks

• Topical antihistamine ointments (e.g., diphenhydramine cream) - can cause further sensitization
• "Caine" topical anesthetics (benzocaine) - sensitization risk

Prevention for Future Mango Work

• Wear nitrile gloves and long sleeves during harvesting
• Wash hands and forearms immediately with soap and water after contact with mango sap
• The mango flesh (pulp) has very low urushiol - most sensitized people can eat the fruit safely as long as someone else peels it
• Once sensitized, reactions tend to occur faster and with less exposure each time

When to See a Doctor Urgently

• Rash spreads to face, eyes, or genitals
• Severe swelling or difficulty breathing (anaphylaxis - rare)
• Signs of secondary infection: pus, increasing redness, warmth, fever
• No improvement after 2-3 weeks

Note: This is clinical guidance based on the image and history provided. For a definitive diagnosis and prescription treatment, please see a dermatologist or general physician.

Pakistani Brand Names for Mango Contact Dermatitis Treatment

1. Topical Corticosteroid Cream (apply to itchy patches 1-2x daily)

Use on the rash only, not on normal skin. Avoid face. Stop once rash clears.

2. Antihistamine Tablet (for itching - take once daily at night)

3. Calamine Lotion (soothing, apply freely as needed)

Ask at any pharmacy simply for "Calamine Lotion" - it is widely stocked.

Suggested Simple Regimen

Effigenta - What It Is and Can You Use It?

• Betamethasone Dipropionate 0.05% (potent corticosteroid - reduces inflammation and itching)
• Gentamicin Sulphate 0.1% (aminoglycoside antibiotic - kills bacteria)

Can You Use It for Mango Contact Dermatitis?

Verdict

• If your rash is clean with no signs of infection (which it appears to be from your photo) - a plain steroid cream like Mometaderm or Betadip is better. No need for the antibiotic component.
• If you've been scratching and it looks infected - Effigenta is a reasonable choice as it treats both the inflammation and any secondary bacterial infection simultaneously.
• Do not use long-term - betamethasone is a potent steroid; prolonged use causes skin thinning, stretch marks, and rebound flares.
• Apply a thin layer once or twice daily to the affected area only. Stop after the rash clears (usually within 1-2 weeks).

Gentamicin in combination steroid creams can also occasionally cause its own contact sensitization with prolonged use - another reason not to use it longer than necessary.