Case study: Superior oblique muscle enlargement presents as orbital myositis

The patient presented with mild pain, diplopia and mild proptosis in the right eye.

Issue: March 15, 2007

ByKathleen M. Zielinski, MD

ByMark R. Levine, MD, FACS

Mark R. Levine

E.K., a 60-year-old missionary working in Ecuador, developed sudden mild pain, diplopia and mild proptosis in her right eye.

She was seen by local physicians who made a diagnosis of right frontal mucocele. An orbital and sinus exploration was performed via a Lynch incision without success. Since the surgery, the diplopia had increased. She returned to the United States for further evaluation.

Examination by us showed vision to be 20/60 in the right eye pinhole to 20/25 and 20/20 in the left eye. External examination showed a patient with a well-healed Lynch incision in the right superior medial orbit (Figure 1). Exophthalmometry base 94 was 16 and 14, respectively. Extraocular muscle movements showed only restriction in the direction of action of the right inferior oblique muscle. There was no pain on palpation or a mass felt. The rest of the eye exam was within normal limits.

Figure 1: After Lynch excision for presumed frontal sinus mucocele
Patient status after Lynch excision for presumed frontal sinus mucocele. Patient presents with diplopia on upgaze.

Images: Levine MR, Zielinski KM

A CT scan showed an enlarged right superior oblique muscle (Figures 2 and 3). There was no evidence of sinus disease. The initial impression was a superior oblique mass. The differential diagnosis included myositis, parasitic infection, less likely thyroid disease, metastatic disease, AV fistula, lymphoma, Wegener’s disease, sarcoid and collagen vascular disease.

Laboratory tests all came back negative, including third-generation TSH, T3, T4, CBC with differential and eosinophil count, P-ANCA, C-ANCA, ANA, chest X-ray and mammogram.

Due to the size of the right superior oblique, an inferior medial caruncular orbitotomy was performed and a biopsy was taken. Pathology showed edema with chronic inflammation and fibrotic changes consistent with orbital myositis (Figures 4a and 4b).

Postoperatively, the patient was started on 60 mg of prednisone and tapered over 6 weeks. The diplopia rapidly improved without recurrence. A repeat CT scan showed the superior oblique to have returned to normal (Figures 5 to 7).

Discussion

Orbital myositis is a subtype of idiopathic orbital inflammation (pseudotumor). These patients present acute or chronic with orbital pain exacerbated by eye movements and associated with diplopia, proptosis, ptosis, conjunctival injection and periorbital edema. The median age at onset is the mid to late 30s (ranging from 3 to 84 years) with female preponderance.

Any or all the extraocular muscles may be involved in orbital myositis. Siatkowski and colleagues, in the largest published series on idiopathic orbital myositis, found that single muscle involvement was found in 68% of patients, 22% had two affected muscles and 10% had three or more affected muscles.

The lateral rectus was most commonly involved (33%), followed by the medial rectus (29%) and the superior rectus (23%). Oblique involvement was rare, with the inferior oblique affected in 3% of cases and the superior oblique affected in 2% of cases.

This rarity of superior and inferior oblique involvement alone was further supported by Stidham and colleagues with a case presentation of a patient with superior oblique involvement. This was successfully treated with systemic steroids.

Wan and colleagues presented an isolated case of superior oblique enlargement in a series of 30 cases with partial improvement on systemic steroids.

Axial CT scan showing enlargement of right superior oblique muscle.	Axial CT scan showing enlargement of right superior oblique muscle.

Histopathologic slides (magnified 400 times) showing muscle fibers and chronic inflammatory cells.

Orbital myositis is classically associated with tendon involvement with conjunctival injection and edema at the muscle insertion. This is typically a differentiating point in distinguishing it from thyroid disease. Yet the literature supports tendon involvement in only 40% to 53% of cases.

The clinical picture of orbital myositis is supported by standardized A-scan echography and computed tomographic scanning. Affected muscles show enlarged bellies, which may appear irregular, and thickened tendons, with homogenous low internal reflectivity echographically.

In this particular condition and patient, the pertinent narrowed differential includes idiopathic inflammation of the trochlea or superior oblique tendon, Grave’s ophthalmopathy and parasitic infection.

Idiopathic inflammation of the trochlea or superior oblique tendon sheath may be properly termed trochleitis or peritrochleitis. In these cases, a portion of the superior oblique muscle and tendon or tendon sheath is involved. The condition is characterized by an aching in the eye area, which comes over a few days. There is point tenderness in the area of the trochlea or the inside aspect of the superior nasal orbital rim. In some instances, an audible click is present in the fields of action of the inferior and superior oblique muscles. A CT scan and standardized echography demonstrates swelling of the superior oblique muscle and tissue around the trochlea.

In Grave’s ophthalmopathy, muscle involvement is bilateral, and most commonly the inferior rectus and medial rectus are involved. Pain is less common. The obliques may be involved along with the other muscles but are not isolated. CT scanning shows the muscle belly thickening to be fusiform with well-defined borders and with tapering at the tendinous insertion. Echographically, the muscle has irregular high internal reflectivity.

The parasitic infectious agents to be considered are cysticercosis (Taenia solium) and trichinosis (Trichinella spiralis). Cysticercosis is caused by the larvae of the pork tapeworm, which can encyst itself in extraocular muscles. It is endemic in India and Central America. Cyst-like lesions can be defined by using ultrasound and CT imaging.

Trichinosis is a tissue nematode that also encysts in muscles. Eye movement is painful, and eosinophilia is typically present. A history of undercooked pork is helpful.


Patient status after transcaruncular exploration and biopsy of right superior oblique muscle.	CT scan axial and coronals after biopsy and placement of patient on 60 mg prednisone, showing the superior oblique muscle returned to normal.

Overall, patients respond favorably to systemic steroids with initial dosing ranging from 60 mg to 120 mg with a slow taper over weeks to months to avoid recurrences, which may occur in up to 50% of patients.

Characteristics of recurrent orbital myositis include male gender, eyelid retraction, lack of proptosis, horizontal rectus inflammation, multiple muscle inflammation, bilateral involvement with tendon sparing and poor response to nonsteroidal anti-inflammatory drugs or corticosteroids.

In refractory cases, a biopsy should be considered to rule out other causes of myositis. If the diagnosis of idiopathic myositis is confirmed and inflammation persists, steroid-sparing chemotherapeutic agents could be considered. Radiation therapy has not been shown to be effective.

For more information:

Mark R. Levine, MD, FACS, is a clinical professor of ophthalmology in the department of ophthalmology at Case Western Reserve University. He can be reached at University Suburban Health Center, 1611 South Green Road, Suite 306A, South Euclid, OH 44121; 216-291-9770; fax: 216-291-0550; e-mail: mlevine@isgwebnet.com.

Kathleen M. Zielinski, MD, can be reached at 1611 South Green Road, South Euclid, OH 44121; e-mail: szielinski@adelphia.net.

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