Tom Shane, MD
Contributing Editor
A 74 year old male presents to the strabismus service with a chief complaint of binocular horizontal diplopia. The patient states that symptoms progressively worsened over the span of one year. He denies any past ocular history or trauma.
Past medical history is positive for thyroid dysfunction and seizure disorder. The patient is on methimazole along with several anti-convulsant medications. Family history is non-contributory. The patient is a retired veteran and admits to a 45-year history of regular marijuana use. Review of systems is negative.
On clinical examination, the patient is disheveled, alert, and oriented. His visual acuity is 20/30 OD and 20/60 OS. The patient has limited extraocular motility to abduction in both eyes and elevation in the left eye. There is 4mm of proptosis in his left eye. Cover tests reveal a 60 prism diopter left esotropia along with a 5 prism dipoter right hypertropia in primary gaze (figure 1). IOP is normal. Pupils are equal, round, and reactive to light without APD. Anterior segment exam is positive for nuclear sclerotic cataracts OU. The funduscopic exam is normal in both eyes.
Figure 1: Left esotropia
Laboratory exam reveals a TSH of 8.8 and a free T4 of 0.57. Tensilon test is negative. MRI of the brain and orbits demonstrates bilateral enlargement of the medial, superior, and inferior rectus muscles in both eyes (figure 2).
Figure 2: Bilateral medical rectus muscle enlargement secondary to Thyroid Eye Disease
Diagnosis: Complex strabismus secondary to thyroid eye disease
In hopes of improving the patient’s symptoms, he is taken to the operating room for a left medial rectus recession. Forced ductions at the time of surgery reveal limited abduction of the left eye. A Jameson muscle hook is passed underneath the left medical rectus muscle and tension is applied in anticipation of suturing the muscle prior to detachment. Suddenly, tension on the muscle hook is lost as the muscle tears between its tendon and the muscle belly (Figure 3).
Figure 3: The PITS. Muscle-tendon dehiscence with only the medial rectus tendon visible over the muscle hook. The muscle has retracted into the orbit.
Pulled In Two Syndrome (PITS) is a rare complication of adult strabismus surgery (incidence = 1/700 cases).1 Rupture characteristically occurs at the muscle-tendon junction. Predisposing factors effecting muscle tensile strength include age, previous surgery, trauma, or infiltrative disease.2 PITS pathologic specimens demonstrate degenerative/infiltrative changes consistent with these etiologies (figure 4).3
Figure 4: Lymphocyte infiltration of an extraocular muscle in Thyroid Eye Disease
Losing a muscle is one of the most concerning complications of extraocular muscle surgery.4 Whenever possible, immediate localization and suturing of the muscle is recommended.5 Excellent exposure of the muscle can be accomplished using the following tools:
- Malleable retractors, which avoiding tissue damage from forceps
- Fiberoptic headlamps, which give adequate illumination in deep orbital dissection
- Operating microscope, which allows good illumination and view for both primary and assistant surgeons.
Lost extraocular muscles can usually be found at their penetration sites into Tenon’s capsule or along the orbital wall. Surgeons must avoid searching along the curve of the globe, which misses the muscle and risks damage to the optic nerve. Once the muscle is isolated with locking bites, it can be sewn back to the eye in hang-back fashion, with an adjustable suture if possible.
If a muscle cannot be found at the time of surgery, a CT scan will oftentimes reveal its location in preparation for a re-operation. Reattachment should take place as soon as possible to avoid further muscle contraction and fibrosis in its lost position. If the muscle cannot be found, a transposition procedure may improve alignment in some cases.
The best way to treat Pulled In Two Syndrome is prevention.6 Preoperatively, doctors must recognize patients who are at higher risk for this complication (due to age, infiltrative disease, or previous trauma). Intraoperatively, prevention can be achieved by using an instrument currently in development: a muscle tension scale. Similar to a fish scale, this device provides controlled and measurable tension on extraocular muscles. This technology can be used to avoid excessive tension on extraocular muscles in patients susceptible to the PITS. Work is currently being done to improve the accuracy of the muscle tension scale throughout the physiologic range of motion of the eye.
After PITS occurs in our patient, the muscle belly is immediately isolated at its attachments to Tenon’s capsule (figure 5). The muscle is secured using locking bites with an absorbable vicryl suture, and then reattached to the globe in hang-back fashion. One month post-operatively, the patient has persistent diplopia and a left esotropia measuring 50 prism diopters in primary gaze (figure 6).
Figure 5: Muscle found at penetration site in Tenon’s capsule after PITS.
Figure 6: One month postoperatively
References:
- Wallace DK, Virata SR, Mukherji SK. “Strabismus Surgery Complicated By “Pulled In Two Syndrome” In a Case of Breast Carcinoma Metastatic to the Medial REctus Muscle.” J of AAPOS. April 200: 117-119
- Dunbar JA, Lueder GT. “Intraoperative Dehiscence of a Rectus Muscle: Report of Two Cases.” J of AAPOS Sept 1997: 175-177.
- Kowal L, Wutthiphan S, McKelvie P. “The Snapped Inferior Rectus” Aus and New Zealand J of Oph (1998) 26, 29-35.
- Murray AND. “Slipped and Lost Muscles and Other Tales of the Unexpected.” J of AAPOS. June 1998: 133-143
- MacEwen CJ, Lee JP, Fells P. “Aetiology and Management of the ‘Detached’ Rectus Muscle” BJ of Oph 1992, 76: 131-136.
- Comment from Kowal L, Wutthiphan S, McKelvie P. “The Snapped Inferior Rectus” Aus and New Zealand J of Oph (1998) 26, 29-35.
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