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Q1: What is the diagnosis?
The diagnosis is idiopathic hypoparathyroidism with basal ganglia calcification. The serum PTH level is inappropriately low for the degree of hypocalcaemia. Hypocalcaemia could have been worsened by other factors (as mentioned below).
There was associated renal failure, probably from prerenal causes, as the patient was clinically dehydrated and hypotensive, with a low central venous pressure and a high urea to creatinine ratio. Renal ultrasound was normal.
Chronic renal failure with secondary hyperparathyroidism can be a cause of basal ganglia calcification,1 but there would be high circulating parathormone in that case.
Q2: What factors could have worsened the hypocalcaemia in this patient?
Other factors that could have contributed to the hypocalcaemia include hypomagnesaemia, renal failure, and the use of anticonvulsant drugs. Hypomagnesaemia produces hypocalcaemia by reducing parathormone secretion and also by interfering with parathormone action.4 Hypomagnesaemia in our patient was probably caused by a combination of an inadequate intake and acidosis from the accompanying renal failure. Systemic acidosis is known to aggravate magnesium loss in the urine. High dose calcium replacement can lead to calciuria and renal magnesium wasting; hence the serum magnesium in hypoparathyroid patients on treatment needs to be monitored closely.
Phenytoin and phenobarbitone can interfere with vitamin D metabolism.5 These drugs induce hepatic enzymes that convert vitamin D and 25-hydroxyvitamin D into their inactive metabolites. In addition they impair calcium absorption from the gut and also affect the resorption of calcium from bone.
Low albumin may reduce the total serum calcium but it does not affect the ionised calcium levels and hence does not contribute to symptomatic hypocalcaemia.
Q3: What is the differential diagnosis on the computed tomograph of the brain?
The various causes of basal ganglia calcification are listed in box 1. The most important treatable cause is hypoparathyroidism. This is characterised by hypocalcaemia, hyperphosphataemia, and a low serum parathormone. Idiopathic hypoparathyroidism can occur as an isolated condition or it may be part of a polyglandular endocrinopathy (candidiasis, autoimmune hypoadrenalism, and thyroid disease). Pseudohypoparathyroidism is caused by target organ resistance to parathormone. These patients have characteristic clinical features (such as a short fourth metacarpal bone) and high circulating parathormone levels.
Box 1: Causes of basal ganglia calcification
Idiopathic basal ganglia calcification
Hypoparathyroidism Idiopathic (autoimmune) Congenital Post-thyroidectomy
Secondary hyperparathyroidism (in renal disease )
Congenital infections (for example, toxoplasmosis )
Toxins Carbon monoxide Lead poisoning
Idiopathic basal ganglia calcification can occur as a normal variant in elderly people. Other causes include Fahr syndrome (idiopathic cerebrovascular ferrocalcinosis) and Cockayne syndrome (associated with progeria). Basal ganglia calcification can also result from exposure to lead and carbon monoxide.
PROGRESS OF OUR PATIENT
The patient was started on an intravenous calcium infusion. He was also given parenteral magnesium sulphate. His sensorium improved dramatically and he was started on oral calcium and vitamin D supplements. His renal function improved with adequate hydration, and his serum creatinine and urea levels normalised. This confirmed our suspicion that there was underlying prerenal failure. A small dose of levadopa with carbidopa was sufficient to control the extrapyramidal symptoms. He was asymptomatic and normocalcaemic on discharge.
Idiopathic hypoparathyroidism with basal ganglia calcification
Basal ganglia calcification may present with neuropsychiatric manifestations.
Calcific foci in other intracranial sites like the cerebellum and cerebral cortex are often associated features.
Magnesium deficiency can worsen hypocalcaemia.
Frequent estimation of serum magnesium is necessary in patients on treatment for hypoparathyroidism.
If these patients also require long term anticonvulsant treatment, they will need close monitoring of their calcium status.
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