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Show Epidemic Optic Neuropathy Is Evident in the Somalian Population Abdirisak A. Dalmar, PhD, MD, Katherine E. Hodson, MSc, Gordon T. Plant, MD Background: Optic neuropathy epidemics have proven to be a serious public health problem around the world. Recently, documented outbreaks have occurred in Cuba and Tanzania, with almost identical clinical presentation. Investigations of both epidemics have implicated nutritional deficiencies as part of a multifactorial etiology, and thus, it is proposed that there may be many undetected epidemics in other food-deprived nations. Somalia, a country subject to prolonged droughts and civil war, may be at particular risk of nutritional deficits. We conducted a case series in Mogadishu, the Somalian capital, with the aim of identifying and charac-terizing any cases of epidemic optic neuropathy. Methods: Cases were recruited at the Al-Noor Eye Hos-pital, Mogadishu, between 2002 and 2004. Individuals were screened by trained ophthalmic nurses, and a full ophthalmic examination was undertaken by an experi-enced ophthalmologist. Patients also completed a life-style questionnaire to identify any common risk factors. Results: One hundred five acute cases of optic neuropathy were identified. Progression from hyperemia to pallor of the optic discs and greatest visual loss occurred over the first month. Our findings are similar to those reported in the Tanzanian epidemic, including involvement of young patients (mean age: 24 6 5.3 years) and evidence of peripheral neuropathy. Conclusion: Epidemic levels of optic neuropathy are evi-dent in Somalia. The extent of visual loss in the first month emphasizes the need to initiate treatment early in the course of the disease. Training and establishing health surveillance systems in community clinics may form a central component to this strategy. Journal of Neuro-Ophthalmology 2011;31:127-130 doi: 10.1097/WNO.0b013e31820d1604 2011 by North American Neuro-Ophthalmology Society Optic neuropathy epidemics around the world have affected tens of thousands of individuals in the past century. In many cases, poor nutrition or toxic dietary factors have been attributed as central features of the un-derlying etiology. Strachan syndrome, for example, first described in the Caribbean (1) was later documented in Canadian prisoners of war subject to malnourishment in Japanese concentration camps during World War II (2). Tropical ataxic neuropathy (TAN) in Nigeria (3), and a form of acute paralysis known as ‘‘Konzo'' in Democratic Republic of Congo (formerly Zaı¨re) (4), Mozambique (5), and Tanzania (6) was associated with cyanide toxicity sec-ondary to cassava consumption (although in the case of TAN, the link with cyanide intoxication is not well es-tablished). More recently, population-wide B-vitamin de-ficiency, in combination with cassava consumption, tobacco smoking (7,8), and, to a lesser extent, low-level chronic methanol consumption (8), was implicated in an epidemic of optic neuropathy in Cuba. Widespread B-vitamin sup-plementation largely resolved the outbreak (7). The clinical features of the Cuban epidemic closely resemble an out-break in Tanzania, which was first reported in 1988 and is now more appropriately regarded as endemic in the sec-ondary school population in Dar es Salaam (9). Reports from Tanzania (10,11) described bilateral, simultaneous, usually painless, visual failure over 2-12 weeks, loss of nerve fibers in the papillomacular bundle associated with central or cecocentral scotomas, impaired color vision, and peripheral neuropathy. The finding that the Tanzanian epidemic also occurred in a B-vitamin deficient population (A. A. Dalmar et al, unpublished data, 2010) suggests a similar multifactorial etiology to that demonstrated in Cuba. The common involvement of nutritional deficiencies in these epidemics has focused attention on the potential for undetected epidemics occurring in other African countries suffering from food shortages. As a country that has been affected by prolonged droughts and civil war since 1991, and in which agriculture makes up 65% of gross domestic From the National Hospital for Neurology and Neurosurgery (AAD, KEH, GTP), London, United Kingdom; and Al-Noor Eye Hospital, Mogadishu, Somalia. This research was partly funded by the Christoffel-Blindenmission. The authors report no conflicts of interest. Address correspondence to Gordon T. Plant, MD, National Hospital for Neurology and Neurosurgery, Queen Square, London WC1N 3BG, United Kingdom; E-mail: gordon.plant@uclh.nhs.uk Dalmar et al: J Neuro-Ophthalmol 2011; 31: 127-130 127 Original Contribution Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. product (12), Somalia is particularly sensitive to failing crop yields. Generalized poor agricultural performance, sus-pected widespread micronutrient deficiencies, and a diet that is predominantly cereal based suggest that the pop-ulation is at risk of nutritional deficiencies and thus potentially to epidemics of optic neuropathy. No survey of epidemic optic neuropathy has ever been conducted in Somalia. We carried out a case series in Mogadishu, the Somalian capital, with the aim of identifying and characterizing any cases of epidemic optic neuropathy, comparing its features to those presenting in Tanzania. METHODS Based on previous case definitions of epidemic optic neu-ropathy (9), patients were recruited from the Al-Noor Eye Hospital, Mogadishu, Somalia, over a period of 2 years (2002-2004). Nurses trained in interviewing techniques administered a questionnaire concerning sociodemographic character-istics and exposure to any known toxins. The information collected also included date of onset, the duration for visual loss to reach its worst level, past and present medications, food intake and weight loss over the previous few months, and drinking/smoking habits. A full clinical examination was undertaken. A certified ophthalmic nurse determined best-corrected visual acuity and assessed color vision using Ishihara pseudoisochromatic color plates. The principal author charted visual fields on a 1-m tangent screen with the use of 1- to 10-mm red test objects, carried out slit-lamp exami-nation and tonometry, and performed a complete fundu-scopic examination. Data Analysis All data were entered into an Excel data sheet. Double entry was not performed, but all variables were coded and checked, and data cleaning was performed where necessary. The data set was imported into SPSS for Windows software and descriptive statistics generated. Data from Somalia were compared with data collected by the authors in a similar study in Tanzania. Ethics The Ministry of Health, Somalia, granted ethical approval for this research. RESULTS A total of 105 cases were seen over the 2 years of the study, and clinical findings are summarized in Table 1. The mean age (6SD) of the optic neuropathy cases was 24 6 5.3 years, with an almost identical age distribution compared to the Tanzanian epidemic (Fig. 1). Of the affected individuals, 65% were men, and 30% presented within a month of symptom onset. On examination, the optic discs were either normal or had dilated capillaries and blurred margins and over 4 weeks developed temporal pallor with loss of the cecocentral nerve fiber layer. In terms of peripheral symptoms, 59% reported numb-ness in the legs and 29% hearing loss, once again demon-strating similar levels to those seen in Tanzania (Fig. 2). Almost half of cases reported weight loss, and more than 50% (16 of 31) of women of breastfeeding age (age . 16 years) were breast-feeding at the time of symptom onset, but this comprised only 15% of the total study population No common medication or dietary factors were evident. TABLE 1. Characteristics of Somalian epidemic optic neuropathy Clinical Characteristic n (%) Duration of disease ,1 month 31 (30.0) 2-3 months 37 (35.0) 4-6 months 22 (21.0) 7-12 months 13 (12.0) .12 months 2 (2.0) Visual acuity* 6/9 to 6/18 20 (19.0) 6/24 to 6/60 75 (71.5) 5/60 to 3/60 10 (9.5) Severely impaired color vision† 77 (73.0) Burning/numbness in legs 62 (59.0) Self-reported hearing loss 30 (28.5) Reported weight loss 47 (44.7) Breastfeeding 16 (15.2) Smoking 10 (9.5) Stomatitis 28 (26.6) *World Health Organization classification: 6/9 to 6/18 ade-quate vision; 6/24 to 3/60 impaired vision; ,3/60 blind. †Able to read 4 or fewer of the 15 Ishihara plates. FIG. 1. Comparison of age distribution between Somalian and Tanzanian (12) optic neuropathy cases. Somalia = 105 patients; Tanzania = 38 patients. 128 Dalmar et al: J Neuro-Ophthalmol 2011; 31: 127-130 Original Contribution Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. DISCUSSION In contrast to previously published Tanzanian data, which predominantly focused on chronic cases of optic neuropa-thy (10,13), the individuals in this study represent acute cases, with over half presenting within 3 months of onset of symptoms. Our results document progression of the symptoms of optic neuropathy over the first 12 weeks. The prominent features were bilateral loss of visual acuity with central or cecocentral scotomas and diminished color vision. There was evolution of optic disc hyperemia to pallor over the first month. Greatest visual loss occurred during the first 4 weeks and continued to deteriorate over the subsequent 8 weeks. These findings are virtually identical to those re-ported from Tanzania, including similar age groups and associated peripheral neuropathy, and hearing loss. Our data support the hypothesis that the clinical syndrome in Somalia and Tanzania is the same entity. Given their similarity to the Cuban epidemic (7,8), and their shared clinical features with Leber herditary optic neuropathy (14), it seems likely that both the Somalian and Tanzanian optic neuropathies are disorders resulting from mitochondrial dysfunction. This has already been proposed for the Cuban epidemic (7-15). In the Somalian and Tanzanian populations (10,16), smoking prevalence was low, thus suggesting that cyanide toxicity from tobacco smoking plays no role in the etiology of this optic neuropathy. This is in contrast to the Cuban epidemic in which smoking was an important risk factor for optic neuropathy (7,8). In Cuba, the underlying mechanism was thought to involve inhibition of oxidative phosphory-lation due to a combination of the following: 1) cyanide from tobacco smoking and/or cassava consumption; 2) formate accumulation due to methanol consumption; and 3) B-vitamin deficiency affecting the detoxification of en-dogenous formate (8,15). This combination of factors would lead to inhibition of adenosine triphosphate (ATP) production, on which neuronal activity is dependent. In the absence of ATP, mitochondrial transport to the site of energy requirement (the nodes of Ranvier and distal axon terminal) cannot occur, leading to neuronal degeneration (15). Papillomacular bundle nerve fibers and long axons have particularly high ATP requirements and may be se-lectively targeted by this mechanism (15). A common feature of the Somalian and Cuban epi-demics is weight loss reported at onset of symptoms, sug-gesting a possible nutritional deficiency with stomatitis occurring in almost one third of our patient cohort. B-vitamin deficiency (riboflavin, niacin, vitamin B6, and vitamin B12) may play a causal role. However, given the lack of a control group in our study and the poor nutritional status of the Somalian population in general, the role of B vitamins in the etiology of Somalian optic neuropathy remains uncertain. Previous studies in Tanzania have suggested that lacta-tion is particularly a strong risk factor for optic neuropathy (13). In our study, more than 50% of women of breast-feeding age reported the onset of optic neuropathy with initiation of lactation. If epidemic optic neuropathy is as-sociated with nutritional deficiencies, the increased de-mands of pregnancy followed by lactation might also be a contributing factor. With optic neuropathy in Tanzania now classed as endemic (9), and evidence presented here for the first time of its prevalence in Somalia, more effective treatment strategies are required. Current treatment of B-vitamin supplementation based on its use in the Cuban epidemic (7,8) has proven very successful in acute cases in Tanzania (Dalmar et al, unpublished data, 2010), and the large extent of visual loss reported over the first month in Somalia places emphasis on the need for early diagnosis and treatment through Training community eye care workers. Establishing a surveillance system in community health clinics to provide data on patterns of disease occurrence and monitor any changes. Developing national guidelines for the treatment and prevention of epidemic optic neuropathy. ACKNOWLEDGMENTS The authors thank all the staff at the Al-Noor Eye Hospital, Mogadishu, and especially manager Mrs Anab Hussein Jama, for their kind support during data collection. REFERENCES 1. Strachan H. On a form of multiple neuritis prevalent in the West Indies. Practitioner. 1897;59:477-484. 2. Fisher C. Residual neuropathological changes in Canadians held prisoners of war by the Japanese (Strachan's disease). Can Serv Med J. 1955;11:157-199. 3. Osuntokun BO. Cassava diet, chronic cyanide intoxication and neuropathy in Nigerian Africans. World Rev Nutr Diet. 1981;36:141-173. FIG. 2. Comparison of peripheral characteristics in Somalian and Tanzanian (12) optic neuropathy cases. Somalia = 105 patients; Tanzania = 38 patients. 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Epidemic of bilateral optic neuropathy in Dar es Salaam, Tanzania. N Engl J Med. 1998; 338:1547-1548. 14. Newman NJ, Wallace DC. Mitochondria and Leber's hereditary optic neuropathy. Am J Ophthalmol. 1990;109: 726-730. 15 Sadun AA. Acquired mitochondrial impairment as a cause of optic nerve disease. Trans Am Ophthalmol Soc. 1998;96: 881-923. 16. Plant GT, Dolin P, Mohamed AA, Mlingi N. Confirmation that neither cyanide intoxication nor mutations commonly associated with Leber's hereditary optic neuropathy are implicated in Tanzanian epidemic optic neuropathy. J Neurol Sci. 1997;152:107-108. 130 Dalmar et al: J Neuro-Ophthalmol 2011; 31: 127-130 Original Contribution Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. [VBvitamindeficiencies] |
