paragraphs verbatim from Marx’ Oral Pathology textbook

In 1937, an otolaryngologist named Eagle reported two cases of neck pain associated with an elongated styloid process.  he followed this in 1948 with a report of several additional cases and declared that they represented a new syndrome.  These cases and the ones seen today all have what appears to be an elongated styloid process and neck pain, particularly upon rotation, flexion, and swallowing.  However, careful radiographic review will reveal a radiolucent separation between the original styloid process and what seems to be a calcified stylohyoid ligament sometimes all the way to the lesser horn of the hyoid bone. Since Eagle’s original description, many of these ‘calcified” stylohyoid ligaments have been removed (something Eagle did not do) and found to be ossified with mature bone rather than calcified with dystrophic calcification.  In addition, if neck C-spine radiographs are taken (something else Eagle did not do) or a computed tomography (CT) scan is taken, one can see that nearly all of the intervertebral ligaments also are ossified.  Indeed, in most of these individuals a careful history will identify paresthesias or pain in their arms, hands, or fingers consistent with a cervical nerve root radiculopathy.  Because the focus of oral and maxillofacial specialists and of other specialists is on the neck pain complaints and because a panoramic radiograph will reveal a long styloid process, the concept of Eagle Syndrome has prevailed, yet this presentation is only proof of a generalized tendency for all true ligaments to become ossified and is known as diffuse interosseous skeletal hypertrophy (DISH).   DISH syndrome is suspected to be a reactive immune-based disease similar to myositis ossificans but targeting only ligaments.

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Selections from pages 198-199…
Diff Dx-   Neck pain and dysphagia is always a worrisome finding.  The clinician should consider malignancies such as squamous cell carcinoma or lymphoepithelioma in this area, as well as salivary gland malignancies.  If the patient is a fair-skinned woman, the
Plummer-Vinson syndrome of iron deficiency anemia with dysphagia due to esophageal webs, which carries a high risk for pharyngeal carcinoma, becomes a consideration.  In any individual with a history of whiplash trauma, ligamental injuries with inflammation is possible.  And of course rheumatoid arthritis, juvenile rheumatoid arthritis, and age-related degenerative joint diseases must also be considered.

Dx Work-up:

Individuals with DISH syndrome will exhibit radiographically identifiable ossifications of their intervertebral ligaments.  Many of these can be seen on a routine panoramic radiograph that includes the cervical spine in the field.   Otherwise, oblique plain neck radiographs or tomographs will show them well and a CT scan will provide the most obvious and detailed picture.   A CT scan is recommended in all cases, not only to identify the intervertebral ossifications but to rule out subtle masses suggestive of malignancy or signs of actual joint-related arthritis.  if the Plummer-Vinson syndrome is considered, a barium swallow study may be useful as well as a CBC with Wintrobe indices.  If rheumatoid arthritis is a serious consideration, a serum ANA and an RF test may be useful.Tx:
The identification of symptomatic “elongated” or “calcified”  (they are actually ossified) stylohyoid ligaments that are proven to be DISH by vertebral radiographs should be co-managed with a rheumatologist.  While it is reasonable to consider excision of the ossified stylohyoid ligaments, this should be accomplished within the context of a more comprehensive management.  DISH is incurable and slowly progressive.  the goal of therapy is to relieve pain and maintain motion and activity.  Cervical collars, neck or back braces, and physical therapy are usually needed for the vertebral involvements.  Patients also benefit from non-steroidal anti-inflammatory drugs.Because nearly every vertebrae will have some ossifying of its respective intervertebral ligaments, cervical surgery is not helpful and therefore not indicated.  However, excising the ossified stylohyoid ligaments can reduce pain, particularly the pain on swallowing.   The patient should be informed that such surgery will not relieve all and perhaps not even the majority of the pain because of the numerous vertebrae affected.The surgical approach is via a horizontal incision within a skin fold of the neck paralleling the inferior border of the mandible.  the incision should be located over the lower portion of the submandibular gland in the area of the intermediate tendon.  The dissection should proceed through the platysma and the superficial layer of the deep cervical fascia to identify the intermediate tendon between the anterior and posterior digastric muscles.  the intermediate tendon is then followed inferiorly for about 1cm to the lesser horn of the hyoid bone.   In some cases, the entire length of the stylohyoid ligament will have ossified, thereby fixing the hyoid in position via one solid cord of bone from the stylomastoid foramen area to the lesser horn of the hyoid.   The ossified stylohyoid ligament is then followed inferiorly for about 1cm to identify the stylohyoid muscle, which lies superficial to the posterior digastric muscle, and to identify the lesser horn of the hyoid.  The ossified stylohyoid ligament is then followed superior from the lesser horn of the hyoid.  the ligament will be just deep to the stylohyoid muscle.  the soft tissues are separated from the ossified stylohyoid ligament before it is separated from the styloid process proper.  This includes ligating the facial artery, which courses deep to the stylohyoid ligament to enter the submandibular triangle.  removal of the ossified stylohyoid ligament can be accomplished with a rongeur or an osteotome and is straightforward because the ossified stylohyoid ligament is usually connected to the native styloid process by a fibrous
band in a pseudo joint fashion.   the residual styloid process is rounded off before closing in layers.Because the stylohyoid ligament is ossified to or nearly to the hyoid bone and because the facial artery and retromandibular vein are in close approximation, a transoral approach is not recommended.  transoral approaches have not been able to completely remove the diseased ligament and significant bleeding with limited access to control it has been encountered.Prognosis:
Excision of the ossified stylohyoid process provides some pain relief and may improve swallowing.   Patients should be informed of the slowly progressive nature of DISH and followed lifelong.  they also must be made aware that continuing physical therapy and medications will be necessary.