Craniofacial bone atrophy in Parry Romberg syndrome demonstrated using a Bayesian hierarchical model.

PURPOSE: Parry Romberg syndrome (PRS) is a condition characterized by progressive hemifacial atrophy, predominantly affecting the soft tissues. Associated bone retraction is a common clinical feature of PRS but has never been assessed. Here we used 3D imaging and Bayesian statistics in order to demonstrate and quantify bone atrophy in PRS. MATERIALS AND METHODS: Ten non-operated patients with PRS (4/10 males) and 12 age-matched controls (7/12 males) were included into the study. The average age at CT-scan was 9.67 +/- 4.13 years for PRS patients and 12.5 +/- 4.37 years for controls. Soft and hard tissue atrophy levels were quantified using computed tomography scans, based on the distances between surfaces of the affected side and the non-affected contralateral side, both for the skin and the bone. We used a hierarchical Bayesian model with clinical priors in order to assess the relationship between hard and soft tissue atrophies. RESULTS: PRS patients had significant hard tissue atrophy, and atrophy extents were similar for soft and hard tissues. There was a trend for a correlation between the extent of hard tissue retraction and the extent of soft tissue retraction, and we could not demonstrate that the relationship between hard and soft tissue retractions was different in PRS and controls. CONCLUSION: Our results indicated that bone atrophy was most probably a primary process rather than a phenomenon secondary to soft tissue retraction. We have provided the first assessment of bone atrophy in PRS patients using Bayesian statistics.