Subconjunctival orbital fat prolapse and thyroid associated orbitopathy: a clinical association

Thyroid associated orbitopathy (TAO) comprises a spectrum of well-recognized clinical signs including exophthalmos, eyelid retraction, soft tissue swelling, ocular misalignment, keratopathy as well as a number of less common manifestations. Subconjunctival fat prolapse is a rare clinical condition occurring typically spontaneously in elderly patients with a mean age of 65-72 years. We describe subconjunctival prolapse of orbital fat as an uncommon clinical association of TAO. Observational study of six patients presenting with a subconjunctival protrusion under the lateral canthus in a series of 198 consecutive cases with TAO examined at a tertiary care referral center. A superotemporally located yellowish, very soft, freely mobile subconjunctival protrusion developed unilaterally in two and bilaterally in four patients with TAO (incidence 3.03%). It was one of the presenting manifestations of TAO in four of ten eyes studied and incited the diagnostic work-up for TAO in two of six patients in this series. Magnetic resonance imaging of the orbit indicated fat density in continuity with intraorbital fat in the area of protrusion. A male to female preponderance of 4:2 and an advanced mean age at onset of TAO is noteworthy for these six patients compared to the pool of 192 patients (64.8 versus 51.8 years, respectively, =0.003) not bearing this sign. Subconjunctival orbital fat prolapse, a clinically impressive age-related ocular lesion, may occasionally predominate amid other clinical manifestations of TAO. It is a nonspecific sign developing most commonly among patients with a relatively advanced age at presentation. Awareness of this association may alert to the diagnosis of thyroid orbitopathy and reassure the patient and physician as to the benign character of the lesion.