This patient was diagnosed with idiopathic neuroretinitis after eliminating the possibility of infectious causes, and non-infectious causes, including inflammation disorders, malignant hypertension, and so on. The patient improved with steroid treatment, and multiple myeloma was confirmed in the evaluation of hematological abnormalities during treatment. The case of neuroretinitis associated with multiple myeloma is very rare.

Impaired permeability of the optic disc vasculature, and infectious or inflammatory processes have been proposed to be responsible for the pathogenesis of neuroretinitis [4, 5]. Table 1 lists other entities that may cause neuroretinitis [1, 6].

This process results in optic disc swelling, secondary leakage to the surrounding retina, and serous retinal detachment, followed by the formation of hard exudates at the level of the outer plexiform layer, giving rise to the macular star appearance (often 2–6 weeks after the onset of the initial symptoms). In most cases of neuroretinitis, macular edema, rather than optic disc edema, is largely responsible for vision loss. Hence, the resolution of macular edema and exudates is positively correlated with vision improvement [7]. Classically, disc edema begins to decrease 2 weeks after onset, and by 3 months, most patients experience complete resolution [8].

The idiopathic subtype accounts for nearly half of the cases of neuroretinitis, and consensus on the treatment of this variant is lacking [7]. Idiopathic neuroretinitis can be divided into single isolated and recurrent episodes. Idiopathic neuroretinitis usually occurs once, and most cases demonstrate spontaneous resolution and usually have a favorable prognosis; however, recurrence portends a poorer visual prognosis [9, 10]. Certain clinical features may act as predictors of recurrence in patients with idiopathic neuroretinitis. Greater severity of visual field deficits and other patterns besides central or cecocentral scotoma, preserved visual acuity with a large relative afferent pupil defect, poor recovery of vision, and the absence of prodromal systemic symptoms that usually accompany infectious neuroretinitis has been shown to be predictive factors for recurrence [4].

Depending on the cause, treatment includes steroids, antibiotics, or combination therapy. After excluding an infectious etiology, idiopathic neuroretinitis is treated with steroids during the acute episodes. If the patient is at risk for recurrent idiopathic neuroretinitis, intravitreal steroid injection and oral or intravenous steroids and immunosuppressive agents may be considered for long-term prophylaxis, which reportedly reduces the frequency of recurrence [7, 10]. As the treatment and prognosis vary according to the cause, ophthalmologists should consider the differential diagnosis of optic disc edema with a macular star, i.e., neuroretinitis masqueraders. Given that neuroretinitis is usually unilateral, a bilateral presentation should make the examiner highly suspicious of a neuroretinitis mimic; however, neuroretinitis cannot be completely ruled out because bilateral cases have been reported [1].

It is not uncommon for masqueraders to be mistaken for neuroretinitis. One study found that 35% of patients referred to a neuro-ophthalmology clinic for the evaluation of neuroretinitis had mimic disorders presenting with optic disc edema with a macular star and were more common than neuroretinitis [3]. Newly diagnosed malignant hypertension was the most common masquerader (43%). Other masqueraders include branch retinal vein occlusion (21%), idiopathic intracranial hypertension (IIH) (14%), diabetic papillopathy (14%), and anterior ischemic optic neuropathy (7%). IIH is one of the conditions that we need to differentiate along with malignant hypertension in neuroretinitis, so when we see a patient with suspected neuroretinitis, it is important to rule out IIH by checking for neurologic symptoms, including headache, nausea/vomiting, visual disturbances such as diplopia, transient visual loss, blurred vision, and hearing impairment, which are common in IIH, performing tests such as brain MRI or CT imaging, MRV and MRA to check for vascular abnormalities such as venous stasis in sinuses, aneurysm, thrombus, and lumbar puncture to measure CSF opening pressure and analyze its components [11] and referral to neurology.

In the present case, the patient had multiple myeloma in addition to neuroretinitis. It is not possible to determine the sequence of occurrence, because the exact timing of the onset of multiple myeloma was unknown. Therefore, it was difficult to determine whether multiple myeloma influenced the development of neuroretinitis. Multiple myeloma is a plasma cell disorder that accounts for 13% of all hematological malignancies and 1% of all neoplastic diseases [12]. Ophthalmic manifestations are a common feature of hematological malignancies and can be divided into two groups: those attributable to the disease’s infiltration of the eye and ocular sequelae due to blood abnormalities. Bouazza et al. reported that ocular manifestations were the most frequent in hematological malignancies such as acute myeloid leukemia (76%), non-Hodgkin’s lymphoma (65.2%), and multiple myeloma (57.6%) [13]. Different ocular lesions such as retinal hemorrhage, Roth spots, and dry eye disease have been reported to be the most common manifestations. Dry eye, retinal hemorrhage, subconjunctival hemorrhage, and central retinal vein occlusion occur in multiple myeloma. Other studies reported the development of dry eye, cataracts, and glaucoma [12, 14].

However, none of the several studies cited above have mentioned the association between multiple myeloma and neuroretinitis. Only one study has investigated the association between the neuroretinitis and multiple myeloma treatment regimens. Lennan et al. [15] reported that a 53-year-old man with multiple myeloma developed severe acute bilateral optic neuroretinitis 8 days after chemotherapy with carmustine, procarbazine, cyclophosphamide, and prednisolone. Procarbazine is known to interfere with neurological function. Carmustine has been reported to interfere transiently with vision. These two drugs raise the possibility that one or both combinations may have caused optic neuropathy. However, since this patient developed neuroretinitis before the treatment of multiple myeloma, our case report is the first description of neuroretinitis associated with multiple myeloma.