Isolated primary amyloidosis of the inferior rectus muscle mimicking Graves’ orbitopathy

Abstract

The diagnosis of Graves’ orbitopathy is usually straightforward. However, orbital diseases that mimick some clinical signs of Graves’ orbitopathy may cause diagnostic confusion, particularly when associated to some form of thyroid dysfunction. This report describes the rare occurrence of localized inferior rectus muscle amyloidosis in a patient with autoimmune hypothyroidism, who was misdiagnosed as Graves’ orbitopathy. A 48-year-old man complained of painless progressive proptosis on the left side and intermittent vertical diplopia for 6 months. The diagnosis of Graves’ orbitopathy was entertained after magnetic resonance imaging revealing a markedly enlarged, tendon-sparing inferior rectus enlargement on the left side, and an autoimmune hypothyroidism was disclosed on systemic medical workup. After no clinical improvement with treatment, the patient was referred to an ophthalmologist and further investigation was performed. The presence of calcification in the inferior rectus muscle on computed tomography, associated with the clinical findings led to a diagnostic biopsy, which revealed amyloid deposition. This report emphasizes that a careful evaluation of atypical forms of Graves’ orbitopathy may be crucial and should include, yet with rare occurrence, amyloidosis in its differential diagnosis.

Clinical and Radiological Features of Intramuscular Orbital Amyloidosis: A Case Series and Literature Review

“…A review of the literature revealed 21 cases of localized EOM amyloidosis and 9 cases of systemic amyloidosis with EOM infiltration (Table 1). 2–29 The most common clinical findings were ophthalmoplegia (63.3%), diplopia (56.7%), and proptosis (30.0%). Patients with systemic amyloidosis were more likely to have multiple muscles affected (55.6% multiple muscles cf 11.1% single muscle involvement).…”

Primary isolated amyloidosis in the extraocular muscle as a rare cause of ophthalmoplegia: A case report and literature review

“…Primary localized amyloidosis in the extraocular muscle is very rare; only 13 such cases without systemic involvement have been reported over the last four decades. 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 In only nine of these was the amyloidosis confined to the extraocular muscles ( Table 1 ), 4 , 5 , 7 , 8 , 10 , 13 , 14 , 15 , 16 whereas the other four cases also exhibited involvement of the soft tissue mass surrounding the enlarged muscles. 6 , 9 , 11 , 12 The nine patients mentioned above ranged from 20 to 80 years old, the enlarged muscles ranged from single to multiple without predilection, and the affected side was unilateral or bilateral.…”

“…Careful interpretation of clinical findings is crucial for correct diagnosis; several cases were initially treated as thyroid eye disease (TED) 14 , 15 since these characteristics of muscle hypertrophy resemble those of TED. Upon computed tomography (CT) or MRI, an enlarged extraocular muscle often appears fusiform, and sharply edged, with tendon sparing.…”

Extraocular muscle enlargement

“…It usually causes tendon sparing fusiform enlargement of the affected muscles [ 138 – 142 ] and can mimic TED particularly when it involves the inferior or medial recti [ 142 , 143 ]. Calcified lesions infiltrating the extraocular muscles can however be seen on CT helping to differentiate it from TED [ 139 , 142 ]. Adjacent hyperostosis and bony irregularity can support a diagnosis of amyloidosis [ 144 ].…”