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Hypoparathyroidism

Causes:

  1. Primary (due to gland failure)
    1. Idiopathic (Autoimmune) (associated with other autoimmune disorders),
       
      Lab tests of Idiopathic hypoparathyroid - Ca2+↓, PO43-↑. (Serum ALP is not raised)
       
      Treatment = alpha calcidiol and calcium supplement.
    2. Infantile hypoparathyroidism: It is associated with thymic aplasia (Di George syndrome)
  2. Secondary
    1. Post operative :  surgery (thyroidectomy).
    2. Post radio iodine therapy
    3. Hypomagnesemia – (Mg is required for PTH secretion)
  3. Pseudohypoparathyroidism (PHP) (Ref. Hari-18th ed., Pg-3118)
    1. It is a group of disorders characterized by hypocalcemia due to renal resistance to PTH.
    2. PTH levels are high.
    3. Various phenotypic abnormalities may be associated—classically, short stature, round face, obesity, short fourth metacarpals, ectopic bone formation, and mental retardation. Cataract.
    4. Treatment is same as for primary.
  4. Pseudopseudohypoparathyroidism (PPHP)
    1. Patients without hypocalcemia but sharing the phenotypic abnormalities (as of pseudo hypoparathyroidism).
    2. These patient have normal serum calcium and high serum PTH.
    3. In pseudohypoparathyroidism, defect lies at PTH receptor level.  While in pseudo pseudohypoparathyroidism defect lies at gene transcription level beyond the PTH receptors.
Mutations in pseudohypoparathyroidism is in gene for Gs-Alpha mostly results in: (AIPG 2011)
  1. In PHP, there is reduced synthesis of cAMP in response to PTH so there is no appropriate increase in the urinary cAMP occurs (AIIMS Nov  2011)
  2. In PPHP there is increased synthesis of cAMP in response to PTH so there is increase in the urinary cAMP occurs. 
  3. Both patterns of inheritance lead to Albright’s hereditary osteodystrophy (AHO), because of haplotype insufficiency—i.e., both copies of Gs alpha must be active in the fetus for normal bone development.

Pseudopseudohypoparathyroidism can be best understood by comparing it to other conditions:

 

Condition

PTH levels

Calcium

Imprinting

Hypoparathyroidism

Low

Low

Not applicable

Pseudohypoparathyroidism

Increase

Low

Gene defect from mother

Pseudopseudohypoparathyroidism

Increase

Normal

Gene defect from father

Tetany 

Definition: Increase excitability of peripheral nerve due either to a low serum calcium or low serum magnesium or alkalosis 

 

 

Note: In CRF, Hypocalcemia is a feature but tetany does not occurs due to acidosis which prevents tetany (MCQ)

 

Causes of tetany

  1. Due to hypocalcemia
    1. Malabsorption                  
    2. Osteomalacia
    3. Hypoparathyroidism                 
    4. Acute pancreatitis
  2. Due to alkalosis (LQ 2012)
    1. Repeated vomiting            
    2. Hyperventilation  
    3. Primary hyperaldosteronism
  3. Hypomagnesemia

Clinical feature of tetany

  1. In children a characteristic triad of     
    1. Carpopedal spasm                    
    2. Stridor         
    3. Convulsions.
  2. In adults complain of tingling in the hands, feet and around the mouth. Carpopedal spasm (Main d’accoucheur position)

Latent tetany signs are

  1. Trousseau’s sign
  2. Chvostek sign

Treatment of tetany

  1. Injection calcium gluconate I/V
  2. In case of persistent vomiting – I/V saline
  3. In hyperventilation – Re breath from same bag




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