What is the management for thickening of the inferior rectus (IR) muscle in the right eye (OD)?

Management of Thickening of the Inferior Rectus Muscle in the Right Eye

Thickening of the inferior rectus muscle in the right eye is most likely due to thyroid eye disease (TED) and requires a stepwise approach starting with medical management, followed by surgical intervention if necessary after the inflammatory phase has stabilized.

Diagnostic Evaluation

Before initiating treatment, proper diagnosis is essential:

• Perform a complete sensorimotor examination to assess mechanical restriction
• Conduct forced duction testing to confirm restriction
• Look for classic signs such as fixation duress (brow elevation and eyelid retraction on attempted elevation)
• Measure exophthalmos with an exophthalmometer
• Screen for optic neuropathy (acuity, color vision, visual fields, pupillary exam, fundus exam)
• Order orbital imaging (CT or MRI) to:
  • Confirm inferior rectus enlargement
  • Evaluate other extraocular muscles for involvement
  • Assess for tendon-sparing enlargement (characteristic of TED)
  • Check for orbital apex crowding
• Order thyroid function tests and thyroid antibodies

Medical Management

1. First-line interventions:

   • Ocular lubricants to combat exposure from eyelid retraction and proptosis 1
   • Punctal plugs if needed for severe dry eye
   • Smoking cessation counseling (critical for patients who smoke)

2. Medical therapy for active inflammation:

   • Teprotumumab (IGF-IR inhibitor) for active TED - reduces proptosis, muscle size, and improves diplopia scores 1
   • Consider selenium supplementation in patients with selenium deficiency for mild TED 1
   • For severe cases with optic neuropathy: high-dose pulse steroid infusion

3. Temporary diplopia management:

   • Fresnel or ground-in prisms for small to moderate deviations 1
   • Chemodenervation (botulinum toxin) during active phase may provide temporary relief 1

Surgical Management

Surgery is indicated for persistent diplopia in primary or reading positions of gaze, but should be delayed until:

• The inflammatory stage has subsided
• The angle of deviation has been stable for at least 4-6 months 1
• MRI confirms disease quiescence (T2, FSE, T1Gad sequences)

Surgical approach for inferior rectus thickening:

• Recession of the restricted inferior rectus muscle is the mainstay of treatment 1
• Consider using:
  • Semi-adjustable suture technique
  • Intentional slight undercorrection with adjustable sutures
  • Wider spreading of the muscle to prevent sagging
  • Permanent polyester sutures to minimize drift

Important Considerations and Pitfalls

1. Orbital decompression considerations:

   • If significant proptosis coexists with strabismus, orbital decompression should be performed before strabismus surgery 1
   • Strabismus surgery after decompression may worsen proptosis

2. Surgical complications to anticipate:

   • Recession of inferior rectus may result in lower lid retraction
   • Risk of consecutive hypertropia after inferior rectus recession
   • Large bilateral inferior rectus recession may result in A-pattern with exotropia in downgaze
   • "Pulled-in-two syndrome" (muscle rupture during surgery) is more common in TED 1

3. Surgical success rates:

   • Vertical strabismus surgery (66% success) is less successful than horizontal strabismus surgery (84%) 1
   • Multiple surgeries may be needed

4. Differential diagnosis considerations:

   • Isolated myositis (though usually affects lateral rectus) 2
   • Orbital hemorrhage (can cause acute inferior rectus thickening) 3
   • Orbital floor fracture with entrapment 4
   • Euthyroid Graves' ophthalmopathy (can present with negative thyroid antibodies initially) 5

Sequence of Interventions

1. Confirm diagnosis and rule out other causes
2. Treat active inflammation with medical therapy
3. Provide symptomatic relief during active phase
4. Monitor for at least 4-6 months of stability
5. Perform strabismus surgery if diplopia persists
6. Consider orbital decompression before strabismus surgery if significant proptosis exists

This approach prioritizes treating the underlying cause while minimizing complications and maximizing the chance of restoring binocular vision and quality of life.