Progressive limitation in mouth opening: Jacob disease

We would like to discuss with you a rare condition known as Jacob disease. The first description of coronoid process enlargement was by Langenbeck1 in 1853, but the first report of an osteochondroma of the coronoid process, forming a pseudojoint between the coronoid process and zygomatic arch, was attributed to the French anatomist Jacob2 in 1899. Currently, only 42 patients of Jacob disease have been reported and confirmed by histologic evidence.3,4 Additionally, to our knowledge, our patient is the sixth typical patient of mushroom-shaped Jacob disease—only 5 similar patients having been reported.5–9