Polyostotic fibrous dysplasia is a rare developmental disorder with focal areas of abnormal bony architecture. We present a case of progressive rib involvement causing severe restrictive pulmonary disease and respiratory failure.
A 59-year-old woman with a history of polyostotic fibrous dysplasia with thoracic cage involvement presented with acute on chronic hypercapnic respiratory failure requiring mechanical ventilation. On physical examination, she was obese with a weight of 201 lbs. The chest wall appeared smaller than expected for patient size, however, no gross deformity was apparent. Breath sounds were reduced over the right lung field. Chest radiographs and thoracic computed tomography scanning revealed marked bony deformities of the rib cage, worse on the right, encroaching on the pulmonary parenchyma. (Images 1: AP chest roentgenogram showing extensive bony abnormalities of the chest with marked decreases in lung volumes. Image 2: Axial computer tomographic image showing massively enlarged irregular ribs impinging on thoracic structures.) The patient improved with intravenous antibiotic coverage for acute bacterial bronchitis, was successfully extubated and discharged home on supplemental oxygen. During outpatient follow-up her pulmonary function tests revealed a severe restrictive ventilatory defect. Total lung capacity (TLC) of 1.53 liters (35% predicted) and vital capacity (VC) of 0.79 liters (30% predicted). Room air pulse oximetry showed a saturation of 92% at rest with symptomatic desaturation to 85% with ambulation. She was managed with continued supplemental oxygen at 3 liters/minute.
Fibrous dysplasia is a sporadic developmental condition affecting bony architecture. Woven bone and calcified cartilage forms in areas where lamellar bone would usually develop. This is accompanied by intense marrow fibrosis and a high rate of bone turnover. Affected bones demonstrate poor mechanical strength leading to pathologic fractures and progressively enlarging deformities that impinge on adjacent structures. Monostotic involvement occurs more commonly than the polyostotic form. The triad of polyostotic fibrous dysplasia, distinctive café-au-lait skin pigmentation and precocious puberty characterizes the McCune-Albright Syndrome. Genomic analysis of patients with McCune-Albright Syndrome has demonstrated mutations in the genes encoding the alpha subunit of the stimulatory guanine-nucleotide–binding protein (Gs-alpha).1 The mutations cause increased activation of the cyclic AMP-protein kinase A signal transduction pathway. It is postulated that the somatic mutations are postzygotic, occurring during early embryogenesis. Mutations at that juncture cause a mosaic pattern where some tissues become affected while others develop normally. Bony involvement in polyostotic fibrous dysplasia typically involves facial bones, skull base, long bones and occasionally ribs. Clinically, patients present with localized pain, pathologic fractures, cranial nerve abnormalities, and rarely high-output cardiac failure resembling Paget’s disease. Malignant transformation occurs with a frequency of less than 1 percent. Typical radiological changes include increased bony radiolucency, focal thinning of the cortex, bony enlargement and deformity. In our review of the literature only two other cases of polyostotic fibrous dysplasia causing restrictive lung disease and respiratory insufficiency have been described.2,3 Surgical resection was employed in both cases to relieve dyspnea and improve the restrictive ventilatory defect.
Polyostotic fibrous dysplasia is a rare cause of progressive chest wall related restrictive lung disease with distinctive radiological findings. In severe cases surgical resection has been attempted for palliation.
M.D. Suskin, None.