Thyroid Ophthalmopathy

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Thyroid Ophthalmopathy
Classification and external resources
ICD-9 242.90



Disease entity

  • ICD 242.90- 242.91

Disease

Thyroid eye disease also known as Thyroid associated ophthmopathy(TAO) or Grave’s orbitopathy is an autoimmune disorder characterised by enlargement of the extraocular muscles and increase in fatty or connective tissue volume.

Etiology

It’s generally associated with Hyperthyroidism but can also be associated with Hypothyroidism and Euthyroidism. The thyroid abnormalities do not cause orbital disease. Thus, treatment of thyroid dysfunction does not necessarily affect course of Grave’s ophthalmopathy.

Risk Factors

  • Cigarette smoking is a strong risk factor for TAO.
  • Patients treated with I131 are at increased risk of developing TAO.

Epidemiology

TAO is more evenly distributed among men and women. It generally presents during 4th and 5th decade of life while it can affect neonates and elderly.

Pathophysiology

The circulating antithyroglobulin, autoantibodies react with thyroid derived thyroglobin attached to eye muscle membranes. The interstitial spaces of muscle show infiltration of mononuclear cells, fibroblasts and accumulation of oedematous fluid. There is deposition of glycosaminoglycans which bind water and contribute to tissue oedema leading to exophthalmos

History/Symptoms

The patient complains of gritty sensations, photophobia, lacrimation, discomfort, forward protrusion of the eye.

In advanced cases, patient complains of dysfunctional eye motility or diminution of vision.

Signs

  • Lid retraction i.e. Dalrymple’s sign occurs in 37-92% patients.
  • Lid lag of the upper eyelid on downward gaze i.e. Von graffe’s sign and lid oedema.
  • TAO is the most common cause for both unilateral and bilateral axial proptosis. There is increased resistance to retropulsion. Hertel’s exophthalmometer is used for the measurement of proptosis.
  • Bulbar conjunctiva can have deep injection i.e. goldzeiher’s sign. Exposure keratitis can occur further due to lagophthalmos which is a major cause for diminution of vision in TAO apart from compressive optic neuropathy.
  • Extraocular muscles are involved in TAO. The most commonly affected muscle is Inferior rectus followed by medial, superior, levator and lateral rectus. The muscles affected results in ocular misalignment, diplopia. Inability to look up when the eye is adducted i.e. double elevator palsy.
  • Compressive optic neuropathy occurs in <5% of patients with typical TED resulting in slowly progressive fulminant visual loss. It occurs due to compression from the oversized recti and orbital fat causing compartment syndrome at the apex of orbit. It is characterised by decrease in vision, colour vision, contrast sensitivity and relative afferent papillary defect. The characteristic visual fields show central scotoma with inferior arcuate defects. The optic nerve head examination may vary from being normal to having disc oedema, pallor or optic atrophy.
    • Clinical course: It is a self limited disease which stabilizes over a period of 3-5 years.
      1. Initial phase- inflammatory phase with orbital and periorbital signs i.e. proptosis and retraction.
      2. Static phase- decrease in the inflammatory phase and minimal improvement.
      3. Quiescent phase- gradual improvement with improved motility and retraction of the muscles

Diagnostic procedures

Laboratory test

The diagnosis can be done clinically with the characteristic clinical picture, restrictive nature of the disease and associated systemic thyroid disease. Though not diagnostic, thyroid hormone levels, thyroid stimulating immunoglobulins, anti thyroid antibodies can be suggestive of diagnosis.

Ultrasonography

On cross section, there is an increase in thickness of the extraocular muscles.

Computed tomography scan

It demonstrates enlargement of the bellies and sparing of the tendons. It helps in assessing the relationship between the optic nerve and muscles at the apex which helps in planning for the surgical intervention if needed.

Magnetic resonance imaging

It again demonstrates fusiform rectus enlargement and orbital fat expansion. It assesses water content in the muscles which correlates with the active inflammation.

Differential diagnosis

  • Orbital pseudotumour
  • Caroticocavernous fistula

Management

Conservative

To quit smoking- this has been proved to be the most important reversible factor. Though not proven but normalisation of thyroid levels can be done. For corneal exposure, lubricants, taping and protective shields can be tried and if necessary tarsorrhapphy can be done. For diplopia, Fresnel prisms or occlusion therapy should be considered.

Systemic steroids

To decrease orbital inflammation oral steroids in a dose of 1- 1.5 mg/ kg can be given for a suggested maximum period of 2 months. Intravenous pulse methyl prednisolone can be considered as an alternative.

Radiation

The radiation therapy works on the similar mechanism of decreasing inflammation. Typical dose of 2000 rad for each orbit 200rad/ day given over a period 10 days. It generally improves vertical motility. Radiation retinopathy can occur as a side effect.

Orbital decompression

It enlarges the existing space by partial removal of bony walls and periosteum. The most commonly done decompression involves the posteromedial wall followed by floor and lateral wall.

Additional Resources

References

  1. Principles and practice of Ophthalmogy; Albert and jakobiec’s by Albert D M, Miller J W; 3rd edition- chapter 229- 230: page 2913-37.
  2. Neurophthalmology: The requisites in Ophthalmology- Martin T, Corbett J- chapter 8: page 145-149.
  3. Basic and clinical science course; section 5 Neurophthalmology American academy of Ophthalmology:2009-10; chapter 14: page 331-334.
  4. Trobe JD, Glaser JS, Laflamme P. Dysthyroid optic neuropathy. Clinical profile and rationale for management. Arch Ophthalmol. 1978 Jul;96(7):1199–1209