Multimodal Imaging of West African Crystalline Maculopathy in an Igbo Man

Abstract

Purpose:

This report describes a case of West African crystalline maculopathy.

Methods:

A case report is presented.

Results:

A 71-year-old Nigerian man was referred for evaluation of bilateral crystalline retinal deposits seen on routine examination. The patient had no acute visual symptoms and no significant ocular history except for cataract extraction and intraocular lens implantation in both eyes. Dilated fundocscopic examination was notable for bilateral greenish-yellow, foveocentric intraretinal crystalline deposits, which were visible on color fundus photography, multicolor confocal scanning laser ophthalmoscopy, and spectral-domain optical coherance tomography. The crystalline deposits were not associated with abnormal short-wavelength autofluorescence or fluorescein angiography findings.

Conclusions:

A diagnosis of West African crystalline maculopathy was made after other causes of crystalline maculopathy were excluded.

Introduction

West African crystalline maculopathy (WACM) is a rare idiopathic maculopathy that has been described in individuals from West Africa. Fewer than 30 cases have been reported in the literature. WACM is characterized by greenish-yellow, foveocentric crystalline deposits. The pathophysiology of WACM and the composition of the foveocentric crystalline deposits in this condition remain poorly understood. The long-term morbidity of WACM is also unknown. We present multimodal imaging of WACM in a 71-year-old Nigerian man. In this report, we describe the first, to our knowledge, multicolor confocal scanning laser ophthalmoscopy and short-wavelength autofluorescence images of eyes with WACM. We also review the current literature.

Methods

Case Report

A 71-year-old Nigerian man of Igbo ethnicity was referred for evaluation of a crystalline maculopathy. On presentation, the patient had no ocular complaints aside from longstanding floaters in both eyes. His ocular history was significant for cataract extraction and intraocular lens implantation in both eyes. He was in a good state of general health, taking only albuterol as needed for asthma and prophylactic low-dose aspirin. He had a history of malaria that was treated with either chloroquine or quinine (precise treatment regimen unknown), childhood chronic ear infections treated with homemade cottonseed extract, and anal fissure repair in Nigeria in the 1980s.

On examination, his best-corrected visual acuity was 20/20 in each eye. Examination of the anterior segment was unremarkable. There were no corneal or conjunctival crystals. The patient was pseudophakic in both eyes with clear capsules. Dilated fundoscopic examination revealed bilateral vitreous syneresis, bilateral greenish-yellow intraretinal foveocentric crystalline deposits, and a small chorioretinal scar just along the inferotemporal arcade in the right eye. The crystalline deposits were clearly demonstrated on color fundus photography (FF450, Zeiss) and multicolor, confocal scanning laser ophthalmoscopy images (Spectralis HRA, Heidelberg Engineering) (Figure 1). Spectral-domain optical coherence tomography (Spectralis HRA, Heidelberg Engineering) demonstrated bilateral, hyperreflective inner retinal deposits, which were more prevalent in the left eye (Figure 2). There were no crystal-associated short-wavelength autofluorescence or fluorescein angiography findings (Spectralis HRA, Heidelberg Engineering) (Figure 3).

Figure 1.

(Top) Color fundus photography and (bottom) multicolor scanning laser ophthalmoscopy (SLO) images of the right and left eyes. Parafoveal greenish-yellow crystals are demonstrated in both eyes. A chorioretinal scar is visible along the inferotemporal arcade in the right eye of the SLO image. SLO imaging artifacts are present between the optic nerve and fovea in both eyes. A shadow artifact from a vitreous opacity is apparent inferior to the optic nerve in the left eye.

Figure 2.

Spectral-domain optical coherence tomography of the (top) right and (bottom) left eyes. Inner retinal hyperreflective foci involving the foveal center and parafovea of both eyes are present and are more numerous in the left eye.

Figure 3.

(Top) Short wavelength fundus autofluorescence and (bottom) venous phase fluorescein angiography of the right and left eyes. No autofluorescent or angiographic abnormalities attributable to crystal deposition are noted in either eye. There is a small chorioretinal scar exhibiting staining present along the inferotemporal arcade in the right eye. A shadow artifact from a vitreous opacity is apparent inferior to the optic nerve in the left eye.

Results

Given this patient’s history and examination findings, WACM was the most likely diagnosis. This patient had no history of exposure to agents, such as tamoxifen, canthaxanthin, nitrofurantoin, and talc, known to cause a drug-associated crystalline maculopathy. Although methoxyflurane exposure during this patient’s anal fissure repair cannot be excluded, the appearance and distribution of the crystalline deposits in this case were distinct from the typical appearance of oxalate crystal deposition after prolonged methoxyflurane exposure. Examination findings and the lack of systemic signs were inconsistent with hyperoxaluria/oxalosis, cystinosis, Sjögren-Larsson syndrome, and an inherited crystalline maculopathy such as Bietti crystalline dystrophy. No diagnostic genetic testing was performed in this case.

WACM is an idiopathic maculopathy first described in 2003 in a case series of 6 individuals of Igbo ethnicity who emigrated from Southeastern Nigeria. ¹ Subsequent reports included cases in individuals from Nigeria, Liberia, Sierra Leone, Ghana, and Guinea. ^{1 -7} Although many cases have been reported in patients older than 50 years, the youngest patient reported to have WACM was a 39-year-old woman from Nigeria. ⁴ Nearly all cases have been bilateral, although markedly asymmetric or unilateral crystalline deposits have been reported. ^4,6

Consistent in all reported WACM cases is the presence of asymptomatic greenish-yellow crystalline deposits located parafoveally. Multicolor, confocal scanning laser ophthalmoscopy nicely highlights the crystals, making them much more obvious than on color fundus photography. Interestingly, there were no crystals visible and no other abnormal findings on autofluorescence in the present case, and this has not been previously reported. As confirmed in our case, optical coherence tomography characteristically reveals hyperreflective inner retinal foci in the fovea. ^{3 -7} Similar to prior reports, the crystalline deposits were not associated with fluorescein angiography findings. ^2,4

Although several have been postulated, the cause of WACM remains elusive. The composition of the crystalline deposits is unknown, but they may be related to xanthophylls. There has been some suggestion that WACM develops as a consequence of blood–retinal barrier compromise. Many of the reported cases had concurrent diabetic retinopathy. WACM has also been reported in patients with sickle cell retinopathy, ^4,5 retinal vein occlusion, ⁴ familial exudative vitreoretinopathy, ⁴ and idiopathic uveitic cystoid macular edema. ⁶ However, there have been cases of WACM, including the present case, in patients without diabetes or retinal vascular disease. ¹

Conclusions

The geographic and ethnic clustering of cases in West Africa raises the possibility of a genetic predisposition or an association with environmental factors. At present, no genetic or environmental factors have been identified. In the initial reported case series, all patients had a history of kola nut ingestion, leading to the suggestion that WACM may be associated with kola nuts. ¹ Even though kola nut ingestion is common in West African populations, later reports described WACM in patients with no known history of kola nut ingestion. ⁴ Interestingly, the patient in the present case had eaten kola nuts nearly every week at social occasions, as is customary in the Igbo culture.

WACM remains poorly understood. In the present case, as in previously reported cases, the crystalline deposits had been visually asymptomatic. Consequently, the crystalline deposits were typically found incidentally. There have been no published reports on possible long-term visual morbidity in WACM. Further studies are necessary to better understand this rare disease entity.