The optic disc granuloma

Granulomatous optic neuropathy is a rare occurrence to the ophthalmologist characterized by infiltration of the optic disc, edema, exudation, peripapillary hemorrhages, or abnormal vasculature.^[1] It is usually associated with profound visual loss, a relative afferent pupillary defect, reduced visual fields, and accompanying features of posterior uveitis, such as retinitis, choroiditis, vasculitis, vascular occlusions, and vitritis; as well as accompanying anterior uveitis in many cases.^[2] Optic disc granulomas are associated with a multitude of disorders, including autoimmune, infectious, neoplastic, and demyelinating diseases, and a multidisciplinary approach is required with a comprehensive ocular examination and a review of systems, as well as appropriate systemic investigations to find out their root cause and treat it.^[2-7] This photo essay describes a unilateral, isolated optic nerve granuloma of unknown origin.

A 42-year-old man presented with sudden, profound visual loss of the right eye for a few days. Visual acuity was counting fingers at 1 foot. The anterior segment showed mild flare and cells in the right eye. A relative afferent pupillary defect was also present. The posterior segment showed a large optic disc granuloma with dilated vessels and exudates with complete loss of recognition of the optic disc [Figure 1a]. A smaller granuloma was noted along the superior vascular arcade with hard exudates. Surprisingly, the vitreous was remarkably clear. The left eye was normal [Figure 1b]. Optic nerve functions were assessed as well, and color vision, contrast sensitivity, and light brightness appreciation were impaired in the right eye. Automated perimetry was not reliable due to poor fixation and vision in the right eye. Optical coherence tomography showed gross disc swelling in the right eye and mild subretinal fluid in the peripapillary region. A posterior subtenon triamcinolone acetonide injection (40 mg/mL) was administered promptly with complete granuloma resolution at 1 month of follow-up and visual restoration to 20/20 at this time [Figure 1c-e]. Complete blood count (normal), erythrocyte sedimentation rate (12 mm/h), C-reactive protein (11300 ng/mL), renal profile, liver profile, and blood glucose were all normal; serum angiotension converting enzyme (56 u/L), venereal disease research laboratory, and toxoplasma IgG and IgM antibodies were negative, along with the Mantoux test and QuantiFERON Gold test. A chest X-ray was also normal. A contrast-enhanced magnetic resonance imaging of the orbit and brain was also normal. All ocular and systemic investigations for uveitis failed to point to an identifiable cause for the granuloma. Although the finding appeared to be so sinister, a single subtenon steroid injection resolved the issue with maintenance of visual acuity, and no recurrence on a follow-up of 16 months, nor was second eye involvement seen. This makes this case unique due to prompt visual acuity restoration upon therapy, complete resolution, and also because no cause has been found for its development.

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Figure 1: (a) Fundus photograph depicting the right optic disc obscured by a granuloma with vascular dilatation, tortuosity and exudation. A smaller granuloma is visible along the superotemporal vascular arcade. (b) The left eye is normal. (c) Granuloma has resolved with appearance of the optic disc and residual gliosis. (d) Optical coherence tomography of the right optic disc at presentation showing gross elevation and mild peripapillary subretinal fluid. (e) Resolution of the granuloma at 16 months of follow-up.

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This is an interesting and unique case of a middle-aged man who presented with gross obliteration of the optic disc by an isolated granuloma, which had to be labeled idiopathic, as no cause could be found after a thorough systemic workup for etiologies associated with granulomatous optic neuropathy. It resolved with a single subtenon steroid injection, fortunately for the patient. Even after a 16-month follow-up, he has not developed a symptomatic illness causative for the optic disc granulomas and remains healthy.

Optic disc granulomas are a rare entity and are caused by vascular, inflammatory, or neoplastic processes. The most common causes reported in literature include sarcoidosis, tuberculosis, Wegener’s granulomatosis, toxocariasis, toxoplasmosis, bartonella, cryptococcosis, Blau syndrome, syphilis, human immunodeficiency virus, leukemia, and lymphoma, to name a few. Optic disc granulomas need to be differentiated from peripapillary choroidal hemangiomas, metastases, amelanotic melanomas, and other tumors.^[3-9]

Granulomatous optic neuropathy has a characteristic lumpy, whitish appearance and raises a red flag for the ophthalmologist. It is accompanied by severe visual loss, albeit painless, and diminished optic nerve function, including color vision, contrast, and visual field loss. Loss of vision is due to infiltration, compression, ischemia of the optic nerve, and associated retinal pathology.^[8] Factors affecting visual outcome are concurrent posterior uveitis, vasculitis, and vascular occlusions, retinal detachment, non-resolution, and vascularization.^[3-9]

In developing countries, tuberculosis and sarcoidosis are more commonly associated with posterior uveitis. Tuberculosis is an airborne infection and a major cause of morbidity and mortality in the world caused by a single organism: Mycobacterium tuberculosis. It is characterized by caseating granulomas. Tubercles of the optic nerve, or tuberculomas, occur in 11.3% of cases and indicate neuro-ophthalmic involvement by this disease, and may be caused by direct infiltration of the optic disc or through hematogenous spread.^[4,10] These may be seen in both immunocompetent and immunocompromised individuals. However, a diagnosis of TB requires a positive purified protein derivative skin test, a chest X-ray, and supporting evidence. Sarcoidosis is a multisystem inflammatory disorder of unknown etiology characterized by the presence of noncaseating granulomata.^[8] Ocular sarcoidosis occurs in <5% of cases, and involvement of the optic nerve is even rarer. Toxocariasis is associated with optic disc granulomas in 6–19% of the cases.^[9]

A thorough workup for systemic etiological disorders with liaison with a medical specialist is needed to establish a correct diagnosis amongst the constellation of diseases known to cause granulomatous infiltration of the optic nerve. This is necessary to institute adequate and appropriate therapy to treat the systemic illness as well as ocular involvement. Subtenon, intravitreal, oral, and intravenous steroids constitute the mainstay of treatment together with other immunosuppressive agents for the treatment of associated systemic diseases. Infectious diseases need anti-infective agents together with ocular steroids for optimal management. Tuberculomas are also responsive to intravitreal anti-vascular endothelial growth factor agents. The prognosis for vision is usually good with appropriate management, especially steroids.^[5-10]

A unilateral isolated optic nerve granuloma is extremely rare, although it paints a grave picture. A thorough workup for its causes should be undertaken with a multidisciplinary approach to find out its cause. Although in this case, the granuloma may be labeled idiopathic as no evidence of systemic disease or malignancy has appeared till the last follow-up.