Differentials
Pseudo-pseudohypoparathyroidism
SIGNS / SYMPTOMS
Patients have Albright's hereditary osteodystrophy without symptoms or signs of PTH hormone resistance.
INVESTIGATIONS
Serum calcium and PTH are normal.
Normal response to exogenous PTH as measured by urine cyclic adenosine monophosphate and urine phosphorus.
Paternal inheritance of causative GNAS mutations (GNAS is the gene that codes for the guanine nucleotide-binding protein Gs-alpha).
Primary hypoparathyroidism
SIGNS / SYMPTOMS
History of prior thyroid gland surgery, multiple transfusions, or Wilson's disease.
Morphological features of DiGeorge syndrome may be present (hypertelorism, micrognathia, short philtrum with fish-mouth appearance, anti-mongoloid slant, telecanthus with short palpebral fissures).
Deafness or blindness suggestive of mitochondrial disease.
May be associated with intellectual disability and delayed development.
INVESTIGATIONS
Parathyroid hormone levels are low with low serum calcium and 25-hydroxyvitamin D levels.
Serum magnesium may be low or elevated.
Secondary hyperparathyroidism
SIGNS / SYMPTOMS
Patients may have chronic kidney disease with fatigue, anorexia, dyspnoea, and oedema.
Children with vitamin D deficiency may have signs of rickets.
INVESTIGATIONS
In people with renal insufficiency, serum creatinine is elevated, with elevated PTH levels produced by decreased calcium and decreased 1,25-dihydroxyvitamin D levels.
Vitamin D deficiency
SIGNS / SYMPTOMS
Symptoms and signs of rickets: hypotonia, bone pain and tenderness, muscle weakness, bow legs and knob knees, Harrison's groove, pigeon deformity of the chest, and kyphoscoliosis. Vitamin D deficiency rickets may mimic PHP in infants, causing elevated PTH level, hypocalcaemia, and hyperphosphatemia. Treatment with vitamin D will normalise these parameters.[46]
INVESTIGATIONS
Low 25-hydroxyvitamin D levels are diagnostic.
Fanconi's syndrome
SIGNS / SYMPTOMS
Causes include sickle cell disease or chemotherapy identified in the history.
INVESTIGATIONS
High urine calcium excretion without elevation of serum phosphate.
Generalised aminoaciduria and glycosuria.
The response of urinary cyclic adenosine monophosphate and phosphate to human PTH is normal.
Fluorosis
SIGNS / SYMPTOMS
Symptoms of bone pain.
INVESTIGATIONS
Serum phosphorus is low to normal.
Patients have increased bone density.
The response of urinary cyclic adenosine monophosphate and phosphate to human PTH is normal.
Osteopetrosis
SIGNS / SYMPTOMS
Family history of osteopetrosis is present.
The infantile form produces growth retardation, failure to thrive, and nasal stuffiness due to malformation of the mastoid and paranasal sinus.
Skull deformities can produce cranial nerve entrapment or hydrocephalus.
The adult form is milder and may be asymptomatic, or produce increased susceptibility to fractures.
Nerve damage produced by bone fractures can cause blindness, facial paralysis, or deafness.
INVESTIGATIONS
Serum phosphorus is low to normal.
Patients have abnormally high bone density.
The response of urinary cyclic adenosine monophosphate and phosphate to human PTH is normal.
Osteosclerosis
SIGNS / SYMPTOMS
No distinguishing clinical features.
INVESTIGATIONS
Serum phosphorus is low to normal.
Patients have abnormally high bone density.
The response of urinary cyclic adenosine monophosphate and phosphate to human PTH is normal.
Familial brachydactyly
SIGNS / SYMPTOMS
Isolated abnormalities of the hand.
INVESTIGATIONS
X-ray reveals shortening of the middle phalanx of all digits.
Serum calcium and phosphorus are normal.
The response of urinary cyclic adenosine monophosphate and phosphate to human PTH is normal.
Prader-Willi syndrome
SIGNS / SYMPTOMS
Patients have poor muscle tone and hyperphagia with a constant feeling of hunger.
INVESTIGATIONS
Genetic testing identifies the causative mutations on chromosome 15.
Serum calcium and phosphate levels are normal.
The response of urinary cyclic adenosine monophosphate and phosphate to human PTH is normal.
Acrodysostosis
SIGNS / SYMPTOMS
Features of the head and face include brachycephaly, a hypoplastic 'pug' nose, maxillary hypoplasia, an open mouth, and epicanthal folds.
INVESTIGATIONS
Serum calcium and phosphate levels are normal.
The response of urinary cyclic adenosine monophosphate and phosphate to human PTH is normal.
Turner's syndrome
SIGNS / SYMPTOMS
Diagnostic morphological features include low-set or malrotated ears, down-sloping eyes, ptosis or hooded eyes, and low posterior hairline. A high-arched palate is also seen.
INVESTIGATIONS
Karyotype reveals 10% or more of the cells with complete or partial loss of a sex chromosome.
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