In the HRCT thorax, there were numerous centrilobular nodules of variable size consisting of very high HU unit compatible with calcium content. Air-space shadows were not seen, and the parenychma architecture remained intact.
In the CT abdomen, there was homogenous hyperdense thickening of epithelial surface, therefore the peritoneal surface. There was sigificant involvement of penile shaft as well.
Diagnosis: metastatic calficification after renal transplant.
Review
Metastatic calcification means deposition of calcium crystal in normal tissue. It differs from dystrophic calcification where the deposition takes place at previously abnormal tissue. It also differs from calciphylaxis which mainly affects the subcutaneous tissue and small vessel. Though the pathogenesis of metastatic calcification is believed to be strongly associated with disorder in calcium homeostasis, exact mechanism is not fully understood. It had been described in condition of primary/ secondary hyperparathyroidism; end-staged renal failure; chronic hemodialysis and disseminated malignancy. In a pathology series, it was found in 60% of patients with chronic hemodialysis.
Since the calcium compound is more favorably formed in alkaline pH, lung is involved most commonly, followed by gastric mucosa and renal tubules. Pulmonary involvement is poorly picked up by simple x-ray as resolution is not enough to tell the calcium content of nodules. The nodules are more common at upper lobe, where the ventilation/ perfusion ratio favor hypocapnea and hence alkaline pH. Apart from interstitial nodules, ground glass pattern may also be seen. Patient may remain asymptomatic, or may suffer from respiratory failure. In contrary to the general belief of benign course, rapidly progressive clinical course leading to organ failure had been reported.
For metastatic calcification related to renal failure, transplant may offer spontaneous regression. However, literature had reported twice for apparent developement of metastatic calcification only after successful renal transplantation. The mechanism was again not known.
This patient died 2 months later due to recurrent severe sepsis.
Reference:
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- Margolin RJ, Addison TE. Hypercalcemia and rapidly progressive respiratiry failure. Chest 1984; 81: 767-769.
- Tam KF, Wong K, Fan WC et al. Metastatic calcification. J HK Coll Radiol 2002; 5: 186-9.
- Breitz HB, Sirotta PA, Nelp WB et al. Progressive pulmonary calcification complicating successful renal transplantation. Am Rev Respir Dis 1987; 136: 1480-82.
- Murris-Espin M, Lacassagne L, Didier A et al. Metastatic pulmonary calcification after renal transplantation. Eur Respir J 1997; 10: 1925-7.