Optic nerve thickening and infarction as the first evidence of orbital involvement with mucormycosis.

We report a 53-year-old female with uncontrolled diabetes mellitus who presented with decreased vision in the right eye for a few hours duration. Orbital computed tomography and magnetic resonance imaging were performed at presentation and showed a thickening and infarction of the right optic nerve with no other orbital abnormalities. A few days later, the patient developed necrosis in the region of the right medial canthus and nasal mucosa. Tissue biopsy confirmed the diagnosis of mucormycosis.

INTRODUCTION

Mucormycosis is an opportunistic fungal infection caused by Mucorales.1 It is a potentially lethal infection that generally affects patients who are immunocompromised due to systemic disease.1 In this case report, we present a middle aged female with rhino- orbito-cerebral mucormycosis who initially presented with thickening and infarction of the right optic nerve and no other orbital abnormalities on orbital imaging few days prior to the development of necrosis in the right medial canthal region and nasal mucosa.

CASE REPORT

A 53-year-old female with poorly controlled diabetes mellitus presented to the emergency room complaining of decreased vision in the right eye that began a few hours prior. Other complaints were redness and swelling of the right cheek for 2 days. Previous ocular history included uncomplicated cataract surgery in the left eye 2 years prior to presentation. Her vital signs were stable. Visual acuity was 20/100 OD and 20/30 OS with a relative afferent pupilary defect on the right side. A mild restriction of ocular motility in all fields of gaze in the right eye was observed. There was no proptosis in either eye. There was marked swelling with mild redness in the lower part of right cheek, with tenderness over the right cheek. There were no signs of abscess. Mild swelling of the right lower lid was present. Fundus examination showed moderate non-proliferative diabetic retinopathy with normal macula and optic disc in both eyes. The rest of the ophthalmic examination was unremarkable. Endoscopic nasal examination showed congested nasal mucosa with no pus or necrosis. Oral cavity examination was normal. The patient was found to have high blood sugar (517 mg/dl) and ketones in the urine. Orbital computed tomography (CT) showed thickening of the right optic nerve with no other orbital abnormalities (no contrast was used as the patient was allergic to the contrast material) [Figure 1]. Para-nasal sinus CT revealed anterior ethmoidal sinus disease, and nicely aerated posterior ethmoidal, sphenoidal and maxillary sinuses bilaterally. The patient was admitted for controlling her diabetes mellitus, management of right cheek cellulitis, and further investigation for the visual loss and restricted ocular motility in the right eye. The patient was started on intravenous amphotericin B, and broad spectrum antibiotics based on clinical suspicion after obtaining blood sample and nasal swab for culture and sensitivity. On the day of admission, magnetic resonance imaging (MRI) was performed. Diffusion-weighted images (DWI) showed high signal intensity along the right optic nerve with hypointense right optic nerve on the apparent diffusion coefficient (ADC) map [Figure 2]. The rest of the orbit, orbital apex, and cavernous sinus were all normal bilaterally [Figure 3]. MRI of the brain was unremarkable. The vision in the right eye decreased dramatically to no light perception with complete external and internal ophthalmoplegia within two days of the initial presentation. The vision and ocular motility continued to remain normal in the left eye. Five days following admission, the patient developed necrosis (eschar) in the right medial canthal region and nasal mucosa. The tissue biopsy confirmed the diagnosis of mucormycosis (Rhizopus organisms). Despite aggressive medical management and wide surgical debridement, the patient died on the 10th day of admission.

Figure 1

(a and b) Axial and coronal orbital computed tomography showing diffuse mild thickening of the right optic nerve with anterior ethmoidal sinus disease

Figure 2

(a) MR imaging showing high signal intensity along right optic nerve on diffusion-weighted images (DWI) (arrow), (b) Apparent diffusion coefficient (ADC) map showing hypointense signal along right optic nerve (arrow). There is no obvious signal-intensity change in the left optic nerve in the DWI (c) and ADC (d)

Figure 3

Magnetic resonance imaging T2 weighted image of the orbit shows normal optic nerve in both sides

DISCUSSION

Rhino-orbito-cerebral mucormycosis is an acute and fulminant infection. Patients present with nonspecific complaints such as headache, low-grade fever, facial swelling, sinusitis, and ocular symptoms. Due to its lethal nature, rhino-orbito-cerebral mucormycosis must be recognized early and treated aggressively without waiting for onset of tissue necrosis.2 Orbital involvement results from spread through the nasolacrimal duct, thin medial orbital wall and presents with proptosis, medial rectus thickening and minimal obliteration of fat shadow.34 Optic nerve infarction that developed two weeks following presentation was previously reported in association with marked orbital inflammatory process in a patient with mucormycosis.5 Here we report a patient who presented with an isolated optic nerve thickening and infarction as the first and only sign of orbital involvement. The infraction of the optic nerve was apparent by orbital MRI findings of high signal intensity along the right optic nerve on DWI, hypointense right optic nerve on ADC map, normal fluid-attenuated inversion recovery (FLAIR) and postcontrast MRI.5 These findings may result from an invasion of the blood vessel walls by the organisms leading to occlusion or thrombosis of the optic nerve sheath, blood vessels, or ophthalmic artery.6 Direct optic nerve infection by mucormycosis may occur. Isolated optic nerve involvement suggests spread of the infection from the primary focus through one of the branches of ophthalmic artery. Thus, optic nerve infarction and thickening may represent the onset of this potentially lethal condition that warrants early and aggressive treatment.