52. Hypoparathyroidism - classification, etiology, pathogenesis, clinical manifestations.

Hypoparathyroidism - classification, etiology, pathogenesis, and clinical manifestations.

Hypoparathyroidism is a condition characterized by deficient secretion or action of parathyroid hormone (PTH), leading to hypocalcemia and hyperphosphatemia.

Classification

1. 1 According to cause

Etiology

Primary hypoparathyroidism

• Surgical removal of parathyroid glands (most common cause), usually during thyroid or neck surgery.
• Autoimmune destruction of parathyroid glands (part of autoimmune polyendocrine syndrome type 1).
• Congenital absence or hypoplasia (e.g., DiGeorge syndrome, 22q11 deletion).
• Radiation-induced damage to the neck.
• Iron or copper deposition (hemochromatosis, Wilson disease).

Pseudohypoparathyroidism

• Genetic defect causing tissue resistance to PTH, usually with high PTH levels.
• Associated with Albright hereditary osteodystrophy (short stature, round face, short metacarpals).

Pathogenesis

Primary hypoparathyroidism

1. Low or absent PTH → decreased osteoclastic bone resorption → reduced calcium release from bones.
2. Decreased renal calcium reabsorption → more calcium lost in urine.
3. Decreased activation of vitamin D → reduced intestinal calcium absorption.
4. Increased phosphate reabsorption in kidneys → hyperphosphatemia.

Pseudohypoparathyroidism

1. PTH secreted normally or in excess.
2. Target organs (bone and kidneys) fail to respond → similar metabolic effects as true deficiency ( hypocalcemia, hyperphosphatemia).

Clinical manifestations

Signs and symptoms of hypocalcemia

• Neuromuscular excitability:
• Tetany: involuntary muscle contractions, carpopedal spasm.
• Chvostek sign: facial muscle twitching when tapping facial nerve.
• Trousseau sign: carpal spasm induced by inflating blood pressure cuff.
• Paresthesias (tingling around mouth and in extremities).
• Muscle cramps and spasms.
• Seizures in severe cases.

Other features

• Dry, coarse skin.
• Brittle nails.
• Hair loss (including eyebrows).
• Dental defects (in children).
• Cataracts (due to chronic low calcium).
• Basal ganglia calcifications → movement disorders.