A Case of Compressive Optic Neuropathy Secondary to Lymphoma of the Extraocular Muscles

ABSTRACT

Compressive optic neuropathy is an urgent condition that may lead to blindness. We report a rare case of compressive optic neuropathy secondary to lymphoma of the extraocular muscles in which the vision was successfully rescued. A 67-year-old man presented with visual acuity of hand motion in the right eye for 1 month. Magnetic resonance imaging demonstrated enlargement of the medial and inferior rectus muscles with their tendons. Tendon enlargement, which is uncommon as Graves’ orbitopathy, motivated us to perform a biopsy. Intravenous steroids following biopsy and chemotherapy after definitive diagnosis allowed for recovery of vision. Clinicians should be aware that enlarged extraocular muscles due to lymphoma can cause compressive optic neuropathy.

Introduction

Non-Hodgkin’s lymphomas constitute up to 55% of all orbital malignancies.¹ Approximately 10% of orbital malignant lymphomas show predominant involvement of the extraocular muscle (EOM),² which rarely results in compressive optic neuropathy (CON). Previously, there have been only three reported cases of compressive optic neuropathy secondary to lymphoma of the EOMs.^3–5 We encountered an additional patient with similar clinical findings and more severe visual deterioration.

Case report

A 67-year-old man presented with diplopia that had been present for one year and blurred vision in the right eye that had been present for one month. His visual acuity was hand motion at 15 cm in the right eye and 20/20 in the left eye. Critical flicker frequency (CFF) was unmeasurable in the right eye and 41 Hz in the left eye. He demonstrated a relative afferent pupillary defect in the right eye. His intraocular pressure was 29 mmHg in the right eye and 20 mmHg in the left eye. He showed mild ptosis of the right eyelid and 7 mm proptosis of the right globe, with limited ocular motility in all directions. Injection and chemosis of the right conjunctiva were also noted (Figure 1A). Fundus examination revealed glaucomatous optic discs in both eyes. No optic nerve swelling or haemorrhages were noted. Goldmann perimetry in the right eye demonstrated a central field defect with an inferior island (Figure 1B).

Figure 1.

(A) Pre-operative photograph of the patient’s face demonstrating right eye proptosis and restriction of movement in all directions. (B) Pre-operative Goldmann perimetry from the right eye.

Magnetic resonance imaging (MRI) demonstrated enlargement of the right medial and inferior rectus muscles with their tendons, compressing the optic nerve at the orbital apex. T1- and T2-weighted images showed isointense enlargement of the right medial and inferior rectus muscles, with respect to grey matter (Figure 2A). T1-weighted images after gadolinium (Gd) administration showed enhancement of the margin of both rectus muscles, including adipose tissue around these muscles (Figure 2B-D); however, they showed no enhancement of the optic nerve or its sheath (Figure 2B-D). The T1-Gd images also demonstrated possible extension into the cavernous sinus through the superior orbital fissure (Figure 2B). Enlargement of the lacrimal gland or infraorbital nerve was not depicted.

Figure 2.

Pre-operative orbital magnetic resonance imaging study. (A) Coronal T1-weighted images showing isointense enlargement of the medial and inferior rectus muscles (arrows). (B) Axial and (C), (D) coronal T1-weighted images after gadolinium administration showing marginal enhancement of the medial and inferior rectus muscles (arrows). The optic nerve (arrowheads) is compressed by the medial rectus muscle, although it shows no gadolinium enhancement. Enhancement of the cavernous sinus (asterisk) suggests tumour extension into this area.

Incisional biopsy of the medial rectus muscle was performed via a transcaruncular approach. A soft, pinkish-grey mass was encountered at the site of the medial rectus muscle. Methylprednisolone pulse therapy (500mg per day for one course of three days) was initiated immediately after surgical biopsy, followed by 30 mg oral prednisolone per day. The patient’s visual acuity improved to 20/25 in the right eye with obvious proptosis reduction (Figure 3A), and the right visual field showed recovery with the exception of the superior nasal step (Figure 3B) at 14 days postoperatively. Because his intraocular pressure was 30 mmHg in the right eye and 24 mmHg in the left eye, topical 0.5% timolol maleate therapy was started bilaterally. At this point, an exotropia due to post-operative swelling of the surgical site and/or paralysis of the medial rectus muscle was noted (Figure 3A).

Figure 3.

(A) Photograph of the patient’s face and (B) Goldman Goldmann perimetry from the right eye at 14 days postoperatively. The proptosis had remarkably reduced, although chemotherapy had not yet been initiated. Exotropia due to post-operative swelling of the surgical site and/or paralysis of the medial rectus muscle is present at this time.

Post-operative immunohistopathological examination revealed hypercellular infiltration of atypical lymphocytes (Figure 4). Clonal rearrangement of the immunoglobulin heavy chain gene was demonstrated by Southern blotting. The definitive diagnosis was diffuse large B-cell lymphoma. After confirming the diagnosis, a THP (pirarubicin)-COP (cyclophosphamide, vincristine, and prednisolone) regimen was initiated by a haematologist in our institution. The Visual acuity in the right eye recovered to 20/20 at 12 months post-operatively, although CFF remained at 23 Hz. The EOM movements in his right eye had improved although the exotropia remained (Figure 5).

Figure 4.

Histological and immunohistochemical photographs of tumour. Hematoxylin and eosin staining, (A) 100× and (B) 400×; (C) anti-CD20 staining, 400 × .

Figure 5.

Photograph of patient’s face at 12 months postoperatively, showing improvement of ocular motility in his right eye.

Discussion

We have described a patient with CON caused by predominant involvement of the EOM in malignant lymphoma. This patient showed the most severe visual deterioration among all reported cases.^3–5 However, prompt diagnosis and treatment enabled visual recovery.

Infiltrative optic neuropathy is a differential diagnosis in patients with lymphoma-induced visual deterioration.⁶ This neuropathy occurs in 5% of patients with lymphoma that exhibits central nervous involvement.⁶ MRI findings in lymphomatous infiltration of the optic nerve include enlargement of the optic nerve and enhancement of the optic nerve sheath;⁶ these were not present in the patient in this case. The absence of optic nerve oedema was also indicative of an absence of optic nerve involvement.

An important differential diagnosis of malignant lymphoma-derived CON is thyroid-associated orbitopathy, which causes 95% of EOM enlargement.^3–5,7 Indeed, one of the reported cases was treated with orbital decompression surgery under misdiagnosis of dysthyroid optic neuropathy.⁴ Thyroid-associated orbitopathy typically manifests as tendon-sparing enlargement of the inferior and medial rectus muscles with upper eyelid retraction.⁸ In contrast, malignant lymphoma most frequently affects the superior rectus muscle, followed by the lateral, inferior, and medial rectus muscles.⁹ For the patient in this case, the uncommon finding of tendon involvement motivated us to perform a biopsy; however, the pattern of EOM involvement in the medial and inferior rectus was characteristic of thyroid-associated orbitopathy. Gadolinium enhancement of the margin of the EOM and adipose tissue around the EOM were also uncommon findings in a thyroid-associated orbitopathy, which was similar to the previous case of orbital diffuse large B-cell lymphoma³; infiltration of lymphoma cells into these regions may have caused ocular motility restriction in all directions.

His Visual acuity improved from hand motion to 20/25 before the initiation of chemotherapy. The visual field also recovered, with the exception of the superior nasal step, possibly due to pre-existing glaucoma. We speculate that steroid administration after surgical biopsy allowed medical decompression, as prednisolone is included in the THP-COP regimen.¹⁰ Because the visual prognosis of CON depends on the duration of symptoms,¹¹ temporary post-operative use of steroids likely protected the optic nerve from irreversible damage before the initiation of chemotherapy. Surgical biopsy itself likely did not contribute to the resolution of CON, because we resected a minimal amount of the tumour in order to avoid worsening his eye movement disorder.

Funding Statement

This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors.

Patient consent and ethics statement

Images have been de-identified, and this patient has provided written informed consent for the publication of these figures.

Declaration of interest statement

No conflicting relationship exists for any author.