Epidemic neuropathy in Cuba: morphological characterization of peripheral nerve lesions in sural nerve biopsies

Exploring the evidence for mitochondrial dysfunction and genetic abnormalities in the etiopathogenesis of tropical ataxic neuropathy

Tropical ataxic neuropathy (TAN) is characterised by ataxic polyneuropathy, degeneration of the posterior columns and pyramidal tracts, optic atrophy, and sensorineural hearing loss. It has been attributed to nutritional/toxic etiologies, but evidence for the same has been equivocal. TAN shares common clinical features with inherited neuropathies and mitochondrial disorders, it may be hypothesised that genetic abnormalities may underlie the pathophysiology of TAN. This study aimed to establish evidence for mitochondrial dysfunction by adopting an integrated biochemical and multipronged genetic analysis. Patients (n = 65) with chronic progressive ataxic neuropathy with involvement of visual and/or auditory pathways underwent deep phenotyping, genetic studies including mitochondrial DNA (mtDNA) deletion analysis, mtDNA and clinical exome sequencing (CES), and respiratory chain complex (RCC) assay. The phenotypic characteristics included dysfunction of visual (n = 14), auditory (n = 12) and visual + auditory pathways (n = 29). Reduced RCC activity was present in 13 patients. Mitochondrial DNA deletions were noted in five patients. Sequencing of mtDNA (n = 45) identified a homoplasmic variant (MT-ND6) and a heteroplasmic variant (MT-COI) in one patient each. CES (n = 45) revealed 55 variants in nuclear genes that are associated with neuropathy (n = 27), deafness (n = 7), ataxia (n = 4), and mitochondrial phenotypes (n = 5) in 36 patients. This study provides preliminary evidence that TAN is associated with a spectrum of genetic abnormalities, including those associated with mitochondrial dysfunction, which is in contradistinction from the prevailing hypothesis that TAN is related to dietary toxins. Analysing the functional relevance of these genetic variants may improve the understanding of the pathogenesis of TAN.

Strachan's syndrome and riboflavin deficiency

Strachan's syndrome comprises a triad of optic, auditory and painful sensory peripheral neuropathy. It has been recognised since the late 19th century and is presumed to result from nutritional deficiency. Patients present acute or subacutely after a period of systemic illness, weight loss or, most commonly, dietary restriction, especially veganism, which can cause riboflavin (vitamin B2) and vitamin B12 deficiencies. The syndrome is more common in people who are black British and often of Jamaican descent. We describe the clinical phenotype using a typical case example, review other endemic nutritional peripheral neuropathies and discuss the potential benefit of riboflavin as a treatment.

Nutritional peripheral neuropathies

Nutritional peripheral neuropathies are a global problem, heavily influenced by geopolitical, cultural and socioeconomic factors. Peripheral neuropathy occurs most frequently secondary to B-vitamin deficiencies, which is suspected to increase in years to come due to the popularity of vegan and vegetarian diets and increased use of bariatric surgery.This review will focus on the common B-vitamins for which a causal link to peripheral neuropathy is more established (vitamins B1, B2, B6, B9 and B12). We will review the historical human and animal data on which much of the clinical descriptions of vitamin deficiencies are based and summarise current available tools for accurately diagnosing a nutritional deficiency. We will also review recently described genetic diseases due to pathogenic variants in genes involved in B-vitamin metabolism that have helped to inform the phenotypes and potential causality of certain B-vitamins in peripheral neuropathy (B2 and B9).Endemic outbreaks of peripheral neuropathy over the last two centuries have been linked to food shortages and nutritional deficiency. These include outbreaks in Jamaican sugar plantation workers in the nineteenth century (Strachan's syndrome), World War two prisoners of war, Cuban endemic neuropathy and also Tanzanian endemic optic neuropathy, which remains a significant public health burden today. An improved understanding of lack of which vitamins cause peripheral neuropathy and how to identify specific deficiencies may lead to prevention of significant and irreversible disability in vulnerable populations.

Tropical spastic paraparesis

A large number of causative agents can result in spinal cord disorders in the tropics including etiologies similar to those of temperate regions such as trauma, spinal bone and disc lesions, tumors, epidural abscess, and congenital malformations. Yet infectious and nutritional disorders differ in their higher prevalence in tropical regions including Pott's disease; brucellosis; neuroborreliosis; various parasitic diseases such as schistosomiasis, neurocysticercosis, and eosinophilic meningitis. Notably, the retrovirus HTLV-1 is the causeof tropical spastic paraparesis/paraplegia or TSP. Nutritional causes of TSP include vitamin B and folate deficiencies, while endemic clusters of konzo and tropical ataxic myeloneuropathy occur in Africa, along with malnutrition and excessive consumption of cyanide-containing bitter cassava. Other toxic etiologies of TSP include lathyrism and fluorosis. Nutritional forms of myelopathy are associated often with optic and sensory neuropathy, hence the name tropical myeloneuropathies. Acute transverse myelopathy, seen in association with vaccination, infections, and fibrocartilaginous embolism of the nucleus pulposus, can be ubiquitous. Multiple sclerosis and optic myelopathy occur in the tropics but with lesser prevalence than in temperate regions. The advent of modern imaging in the tropics, including computed tomography and magnetic resonance imaging, has allowed better diagnosis and treatment of these conditions that are a frequent cause of death and disability. This chapter provides an overview of TSP emphasizing the most common causes with clues to diagnosis and effective therapy.

Epidemics and outbreaks of peripheral nervous system disorders: II. Toxic and nutritional causes

Peripheral neuropathies have various causes, both infectious and non-infectious. When we think of “epidemics”, we often refer to an infectious or even post-infectious origin. Nevertheless, the history of mankind is marked by episodes of epidemics of peripheral neuropathies of non-infectious nature, either of nutritional or toxic origin: we present here the main causes of such epidemics.

Tropical myelopathies

A large number of causal agents produce spinal cord lesions in the tropics. Most etiologies found in temperate regions also occur in the tropics including trauma, herniated discs, tumors, epidural abscess, and congenital malformations. However, infectious and nutritional disorders occur with higher prevalence in tropical regions. Among the most common infectious etiologies are tuberculous Pott's disease, brucellosis, and neuroborreliosis. Parasitic diseases such as schistosomiasis, neurocysticercosis, and eosinophilic meningitis are frequent causes of nontraumatic paraplegia. The retrovirus HTLV-1 is a cause of tropical spastic paraparesis. Nutritional causes of paraparesis include deficiencies of vitamin B12 and folate; endemic clusters of konzo and tropical ataxic myeloneuropathy are associated in Africa with malnutrition and excessive consumption of cyanide-containing bitter cassava. Other toxic etiologies of tropical paraplegia include lathyrism and fluorosis. Nutritional forms of myelopathy are associated often with optic and sensory neuropathy, hence the name tropical myeloneuropathies. Acute transverse myelopathy is seen in association with vaccination, infections, and fibrocartilaginous embolism of the nucleus pulposus. Multiple sclerosis and optic myelopathy occur in the tropics but with lesser prevalence than in temperate regions. The advent of modern imaging in the tropics, including computed tomography and magnetic resonance imaging, has allowed better diagnosis and treatment of these conditions that are a frequent cause of death and disability.

Nutritional disorders in tropical neurology

About three-fourths of the total world population live in the tropics but consume only 6% of worldwide food production and contribute 15% of the world's net revenue explaining the short life expectancy, high infantile mortality, and poor daily caloric intake; moreover, lack of clean drinking water and deficient sanitation promote water-borne infections, diarrhea, and risk of malabsorption that contribute to the prevalence of malnutrition in the tropics. One-third of the world's population consumes insufficient iodine increasing the risk for mental retardation and deafness due to maternal hypothyroidism. The main nutritional syndromes comprise protein-energy malnutrition (marasmus and kwashiorkor); nutritional neuropathies, myelopathies and neuromyelopathies, as well as specific deficiencies of vitamins and micronutrients including iodine, iron, zinc, and selenium.

Interrelationships of undernutrition and neurotoxicity: food for thought and research attention

The neurotoxic actions of chemical agents on humans and animals are usually studied with little consideration of the subject's nutritional status. States of protein-calorie, vitamin and/or mineral undernutrition are associated with a range of neurodevelopmental, neurological and psychiatric disorders, commonly with involvement of both the central and the peripheral nervous system. Undernutrition can modify risk for certain chemical-induced neurologic diseases, and in some cases undernutrition may be a prerequisite for neurotoxicity to surface. In addition, neurologic disease associated with undernutrition or neurotoxicity may show similarities in clinical and neuropathological expression, especially in the peripheral nervous system. The combined effects of undernutrition and chemical neurotoxicity are most relevant to people with low incomes who experience chronic hunger, parasitism and infectious disease, monotonous diets of plants with neurotoxic potential (notably cassava), environmental pollution from rapid industrial development, chronic alcohol abuse, or prolonged treatment with certain therapeutic drugs. Undernutrition alone or in combination with chemical exposure is also important in high-income societies in the setting of drug and alcohol abuse, old age, food faddism, post-bariatric surgery, and drug treatment for certain medical conditions, including cancer and tuberculosis. The nutritional demands of pregnancy and lactation increase the risk of fetal and infant undernutrition and chemical interactions therewith.

Brain barrier dysfunction in Cuban epidemic optic neuropathy

BACKGROUND AND PURPOSE

There are practically no references to cerebrospinal fluid (CSF) studies in tropical or nutritional neuropathies. In the present paper we present the results of CSF studies in patients with Cuban Epidemic Optic Neuropathy (CEON) during epidemic and endemic periods, with an appraisal as to the contribution of brain barriers' function in the pathophysiology of this disease.

METHODS

Two hundred and five patients with CEON were studied during the epidemic period (1992-1993) and 12 patients outside the outbreak (1995-1997). CSF protein determination and electrophoresis were carried out, as well as serum and CSF albumin and immunoglobulin G (IgG) quantitation for calculating IgG and Q(alb) indexes, in order to evaluate intrathecal IgG synthesis and the permeability of the blood-CSF barrier (B-CSF B).

RESULTS

One fourth of the patients had increased permeability of the B-CSF B, but damage was more frequent between 16 and 60 days from onset of disease, disappearing after 120 days. B-CSF B dysfunction was more prevalent in patients with severe neurological impairment, although it was not related to the severity of ophthalmological damage. The group of patients studied outside of the outbreak (endemic period) showed similar results.

DISCUSSION

The possible association of increased permeability of the B-CSF B with oxidative stress, which lies on the basis of this epidemic outbreak, is discussed.

Receding horizons of health: biocultural approaches to public health paradoxes

Worldwide challenges to health reflect a "paradox of success," whereby both the strengths and the weaknesses of current approaches in public health, epidemiology, and biomedicine have determined the nature of the health problems we now face. In detail, we analyze and illustrate five constituent paradoxes that fuel continued health risk even in the face of success, including: (1) unmasking, (2) local biology, (3) socialization, (4) emerging and reemerging disease, and (5) savage inequity. We trace the pathways behind the paradoxes and their effects on health, and demonstrate that biocultural dynamics are involved in each. Furthermore, we track the roots of health paradox to changes that divert or disrupt pathways for production of health. These analyses contribute to an emerging literature of research and praxis on integrative biocultural models of health.

Maternal and infant essential fatty acid status in Havana, Cuba

BACKGROUND

Adequate intake of essential fatty acids (EFAs) is required for optimal development of the central nervous system and visual acuity in infants. Little information exists regarding the EFA status of vulnerable populations living in Southern regions.

OBJECTIVE

We examined the adequacy of EFA status in Cuban breast-feeding mothers and their infants.

DESIGN

Blood and breast-milk samples were obtained from a cross-sectional sample of mothers and term infants in Havana at 2 mo postpartum. We determined the fatty acid profiles of total lipids in breast milk, plasma, and erythrocytes and assessed infant visual acuity by using Teller acuity cards.

RESULTS

Of the 56 mothers and infants examined, none showed biochemical signs of poor EFA status. Compared with values reported in the literature, mothers had an adequate EFA profile in their breast milk, plasma, and erythrocytes. The docosahexaenoic acid (DHA) concentration in breast milk was 0.43 +/- 0.26% of total fatty acids. It appeared that these breast-fed infants had an adequate dietary supply of DHA, as reflected by the mean plasma and erythrocyte DHA concentrations (2.82 +/- 0.84% and 7.41 +/- 1.16% of total fatty acids, respectively). Infant visual acuity testing showed a mean of 2.00 +/- 0.68 cycles/degree, which is within the normal range of mean binocular acuities for 2-mo-old term infants. The data did not show any relation between EFA concentrations and visual acuity.

CONCLUSION

The results suggest that n-3 fatty acid deficiency and potential related deficits in early visual neural development are rare, if they exist at all, in breast-feeding women and their infants in Havana.

Neuromuscular diseases and disorders of the alimentary system

This review outlines the relationship and interaction between neuromuscular diseases and disorders of the alimentary system. Neuromuscular manifestations of gastrointestinal and hepatobiliary diseases are first considered. Such diseases may cause neuromuscular disorders by leading to nutritional deficiency or by more direct mechanisms. The pathogenesis, clinical features, and treatment of these various neuromuscular manifestations are discussed. The impact of disorders of nerve, neuromuscular transmission, and muscle on the alimentary system is then reviewed. The main sequelae are impaired deglutition and gastrointestinal dysmotility. The management of these complications is considered.

Mechanism of enterovirus involvement in epidemic neuropathy: hypothesis regarding pathophysiology

During the epidemic of optic and peripheral neuropathy which occurred in Cuba in 1992-1993, viruses antigenically related to the Coxsackie viruses were isolated from cerebrospinal fluid of patients. Concurrently with the virologic studies, epidemiologic, toxicologic, nutritional, immunologic, and histopathologic investigations were also carried out. Although it was demonstrated that the illness was associated with toxic and nutritional risk factors, it has not been possible to identify a specific etiology for the symptoms observed. Taking into consideration the results obtained in all of the various investigations, we have formulated an integral, multifactorial hypothesis which attempts to explain a pathophysiologic mechanism by which the viruses isolated could participate in the pathogenesis of the illness. We propose that the viral agents produce a persistent infection, and the possibility that they may act as mediator of an autoimmune pathogenic process.

Epidemic neuropathy in Cuba: a public health problem related to the Cuban Democracy Act of the United States

In 1992, the USA embargo on Cuba was tightened through the passage of the Cuban Democracy Act (CDA) that explicitly restricts food and medical supplies. The embargo has contributed to cause a number of public health problems in Cuba including: (1) an epidemic of more than 50,000 cases of optic and peripheral neuropathies in 1992-1993, resulting from dietary deficiency; (2) an epidemic of esophageal stenoses in toddlers who inadvertently drank liquid lye as a result of a soap shortage for which liquid lye was substituted; (3) an outbreak of Guillain-Barré syndrome in Havana, in June and July 1994, resulting from water contamination due to lack of chemicals for water treatment to eliminate Campylobacter sp.; (4) outbreaks of self-inflicted disease and injuries caused by rioting among Cubans detained at the US Naval base at Guantánamo Bay, and (5) a decline in medical practice standards and public health indicators in Cuba resulting from the enactment of the CDA, documented by the American Public Health Association in 1993 and confirmed in March 1997 by the American Association for World Health. Despite this evidence, the Cuban embargo remains a politically sensitive subject in the USA, resistant to public health concerns, as evidenced by the recent passage of the Helms-Burton Act. The public health effects of the CDA need to be reviewed with possible revocation or at least modification.

Tropical myeloneuropathies revisited

An interesting neurological syndrome, characterized by recurrent optic neuritis, cervical myelopathy from syringomyelia, paraparesis, amenorrhea-galactorrhea, and other endocrine problems, has been described among young black women in the French West Indies. The etiology remains unknown, but possible links with Devic's disease, acute disseminated encephalomyelitis, and neurotoxicity from quinolines in Annona muricata teas have been postulated. The largest epidemic of neuropathy in this century occurred in Cuba in 1991-1994. Clinical features and etiologic studies are reviewed. Its primary cause was nutritional. A similar epidemic was recently described in Tanzania. A number of infectious neuropathies and myopathies are reviewed, including leprosy, tuberculosis, hemorrhagic fevers (Ebola and Marburg filoviruses, Lassa, Argentinean and Bolivian arenaviruses), the human retrovirus human T-cell lymphotropic virus type I, Lyme disease and postimmunization neuropathies. The tropics continue to contribute interesting and important clinical conditions that may illuminate the etiopathiogenesis of other common disorders.

An epidemic of optic neuropathy in Tanzania: characterization of the visual disorder and associated peripheral neuropathy

An epidemic of subacute bilateral visual failure has affected large numbers of teenagers and young adult Africans in coastal Tanzania since 1988. Previous work had indicated that many patients had sensory symptoms, but the nature of the neurological involvement was uncertain. The primary objective of this study was to characterize the accompanying neurological disorder. Furthermore, the nature of the visual loss was uncertain from previous reports as both retinopathy and optic neuropathy had been suggested. Full ophthalmic and neurological examinations were carried out at the Muhimbili University Hospital in Dar es Salaam. Nerve conduction studies, pattern electro-retinograms and cortical visually evoked responses and colour contrast sensitivity tests were carried out. Thirty eight young Africans and 12 controls were included in the study. The characteristic fundus picture was symmetrical temporal optic atrophy, and thinning of the caeco-central nerve fibre layer. Fluorescein angiography was normal. The electrophysiological and colour contrast sensitivity tests confirmed optic neuropathy in the majority of cases but primary retinal involvement was indicated in some. Neurological examination and nerve conduction measurements showed evidence of a peripheral neuropathy in 47% of the patients. The peripheral neuropathy is likely to have involved large fibres (from the nerve conduction studies) but the symptoms suggest small fibre loss also. 42% had developed hearing loss. Urinary thiocyanate levels were uniformly low. Serum was negative for antibodies to HTLV-1. DNA analysis from three cases was negative for three known mutations associated with Leber's hereditary optic atrophy (11778, 3460 and 14484). This entity, occurring predominantly in a young age group, does not correspond closely to other tropical neurological syndromes previously described from East Africa although it is clinically very similar to Strachan's syndrome (originally described in the Caribbean and more recently in prisoners of war) and also to an epidemic of optic and peripheral neuropathy that has recently occurred in Cuba. The aetiology has not yet been determined. A micronutrient deficiency is likely but has not been established.

Epidemic optic and peripheral neuropathy in Cuba: a unique geopolitical public health problem

During 1992 and 1993 an epidemic of optic and peripheral neuropathy affected over 50,000 Cubans. This occurred in the unique setting of a communist country which had a widespread health care network and wherein sudden changes in the economy affected most of the population. Although nutritional factors appeared to play a key role in the pathogenesis of the epidemic neuropathy, viral, toxic, and genetic factors were investigated by Cuban and North American scientists. The authors, representing different disciplines and different groups that visited Cuba during the epidemic, review and reflect on the clinical and laboratory findings which became available through their own experience and through reviewing the literature. The recent Cuban epidemic is compared to similar outbreaks of optic and peripheral neuropathy which have occurred in the past.

An epidemic of optic neuropathy and painful sensory neuropathy in Cuba: clinical aspects

An epidemic of bilateral optic neuropathy and painful sensory neuropathy occurred in Cuba in 1991-1993. Over 45,000 individuals were stated to have been affected. We report a clinical study on 25 patients seen in Cuba in 1993-1994. Affected patients showed either bilateral optic neuropathy with caecocentral scotomata or a distal predominantly sensory neuropathy sometimes associated with deafness, or a combination of both optic and peripheral sensory neuropathy. The nature of the epidemic is discussed. The clinical features in patients with confirmed neurological deficits were consistent with a diagnosis of Strachan's syndrome, probably related to nutritional deficiency. Other patients with similar symptoms showed no evidence either of optic or peripheral neuropathy and were considered to represent disease mimicry on a psychoneurotic basis.

An epidemic in Cuba of optic neuropathy, sensorineural deafness, peripheral sensory neuropathy and dorsolateral myeloneuropathy

An epidemic outbreak of peripheral neuropathy affected Cuba in 1992-93 resulting in 50,862 cases (national cumulative incidence rate (CIR) 461.4 per 100,000). Clinical forms included retrobulbar optic neuropathy, sensory and dysautonomic peripheral neuropathy, dorsolateral myeloneuropathy, sensorineural deafness, dysphonia and dysphagia, spastic paraparesis, and mixed forms. For epidemiological purposes, cases were classified as optic forms (CIR 242.39) or peripheral forms (CIR 219.25). Increased risk was found among smokers (odds ratio (OR) 4.9), those with history of missing meals (OR 4.7) resulting in lower intake of animal protein, fat, and foods that contain B-vitamins, combined drinking and smoking (OR 3.5), weight loss (OR 2.8), excessive sugar consumption (OR 2.7) and heavy drinking (OR 2.3). Optic neuropathy was characterized by decreased vision, bilateral and symmetric central or cecocentral scotomata, and loss of color vision due to selective lesion of the maculopapillary bundles. Peripheral neuropathy was a distal axonopathy lesion affecting predominantly large myelinated axons. Deafness produced selective high frequency (4-8 kHz) hearing loss. Myelopathy lesions combined dorsal column deficits and pyramidal involvement of lower limbs with spastic bladder. Clinical features were those of Strachan syndrome and beriberi. Intensive search for neurotoxic agents, in particular organophosphorus esters, chronic cyanide, and trichloroethylene intoxication, yielded negative results. Treatment of patients with B-group vitamins and folate produced rewarding results. Most patients improved significantly and less than 0.1% of them remained with sequelae; there were no fatal cases. Supplementation of multivitamins to the entire Cuban population resulted in curbing of the epidemic. Overt malnutrition was not present, but a deficit of micronutrients, in particular thiamine, cobalamine, folate and sulfur amino acids appears to have been a primary determinant of this epidemic.