Prevalent neuropathy in a cohort of HIV-infected Kenyan sex workers using antiretroviral drugs

Introduction Several risk factors including stavudine and age have been strongly associated with polyneuropathy. However, conflicting data exist on height as an independent risk factor in polyneuropathy. The objective of this study is to exclude height as an independent polyneuropathy risk factor in a cohort of human immunodeficiency virus (HIV)-infected Kenyan sex workers. Methods This was an analysis of prospectively collected data of treatment-naive subjects initiating either stavudine or tenofovir diphosphate fumarate or zidovudine-based antiretroviral therapy (ART) regimens from January 2008 to August 2012. Polyneuropathy was characterised as burning sensation, numbness, or dysesthesia. The study used arithmetic means of weight (kg) and height (cm) measured in duplicates using calibrated scales. Results After exclusion of duplicate data sets and un-confirmed cases of polyneuropathy, the study identified 212 patients without polyneuropathy, 14 pre-ART and 94 post-ART related polyneuropathy cases. Polyneuropathy cases were older but did not differ in demographic, clinical and laboratory parameters at baseline. There was a significant difference in first-line ART regimens with more patients on tenofovir disoproxil fumarate in the post-ART group (p=0.017). Conclusion Polyneuropathy is a common disorder among HIV-infected Kenyan sex workers. These data cannot support the postulated increased risk by height after matching for gender and ART duration. Though stavudine is associated with polyneuropathy, in this study many patients previously not exposed to stavudine developed polyneuropathy. This suggests the involvement of unknown risk factors such as genetic and metabolite differences in the development of polyneuropathy.


Introduction
Global access to antiretroviral therapy (ART) has dramatically lowered the mortality and morbidity rates of human immunodeficiency virus (HIV)-infected patients [1]. However, with substantially expanding life expectancy particularly in resourcelimited settings including Kenya, the burden of polyneuropathy (PN) can complicate the effectiveness of many treatment programs.
Sensory neuropathies including PN are the most frequent neurological disorders associated with HIV infection and its treatment [2]. Because of the severe pain associated this condition, PN severely affects the quality of life and daily function of people living with HIV-infection [3].
Two major types of HIV-associated PN exist: primary HIV-associated [3] or toxic types associated to nucleoside reverse transcriptase inhibitors (NRTIs), particularly the "D-drugs" including zalcitabine (ddC), stavudine (d4T), and didanosine (ddI). Both types of PN affect approximately 30-67% of HIV-infected patients [4,5]. There are no estimates of the burden of HIV-related PN for the Kenyan sex workers whose HIV prevalence is approximately 29.3% [6]. In addition, scarce data exist on risk factors associated with PN among this population. PN is the most frequent ART-related toxicity in sub-Saharan Africa [7,8], especially in older patients [9].
Exposure to d4T is a well-established independent risk factor for PN among many cohorts in both resource-rich [10,11] and resourcelimited settings [8]. However, not all patients receiving d4T end up with PN, suggesting that host factors may play a role in the patient's risk. Widely studied examples of host factors include the presence of mitochondrial haplogroup T [12], genetic markers of host inflammatory responses and cytokine genotypes, notably alleles of tumor necrosis factor-A (TNFA) [13][14][15]. In the general population, several factors including diabetes mellitus, poor glycemic control, male sex, white race, and older age can increase the risk of developing PN [16,17]. In the HIV-infected population, more advanced HIV disease or AIDS, CD4 cell count<100 cells/mm 3 , viral load above 10, 000 copies/ml, past history of neuropathy, use of other neurotoxic drugs e.g. anti-tuberculosis drugs, certain nutritional deficiencies (vitamin B-12 deficiency), co-existing conditions such as diabetes or hepatitis C and alcoholism have been associated with PN [18].
There is adequate literature on some PN-related risk factors such as d4T use, CD4 cell counts, and older age. However, conflicting data exist on how PN is associated with height in the aging HIV-infected population. Whereas several studies have consistently associated height with increased PN risk [19][20][21], other studies have consistently found no association between height and PN [22]. The diagnosis of PN did not require the presence of symptoms in studies where height was not associated with PN [9]. Height has proved to be an important and practical predictor of other forms of neuropathy [17, 22,23]. There are suggestions that it increase the risk of neuropathy because of increased axon surface exposure to toxins [24]. In a study that confirmed height as a risk factor, there was a significant association between height and PN despite their cohort being 5 cm shorter on average than in other ethnic groups [20]. The authors explain this as an influence of longer leg length relative to the trunk length in Black compared with White individuals [25].
The purpose of the current study was to exclude height as an independent risk factor in a cohort of HIV-infected Kenyan sex workers, after matching them for gender and duration of therapy and after excluding other risk factors such as alcohol or diabetes.

Study design
This was a retrospective study that utilized routinely collected data from HIV-infected sex workers at Pumwani clinic were analysed.
Pumwani clinic is part of the sex workers outreach program (SWOP)

Anthropometric measurements
Using calibrated scales, weighing of patients was free of any heavy items and after removing shoes. Measurements of current weight (kg) and height (cm) were in duplicate based on procedures recommended by WHO [27]. We used the arithmetic means obtained from the two measurements then calculated body mass index (BMI) by dividing the weight in kg by the square of the height in metres.

Assessment of neuropathy
The diagnosis of PN relied on clinicians' judgment and at least one of the following lower limb neuropathic clinical symptoms: numbness, dysesthesia, burning sensation, stabbing pain or aching, pins and needles. Clinicians in SWOP clinics have had intensive training in the history, clinical presentation, examination, and treatment of PN. We classified subjects as pre-ART PN if records showed a clinical diagnosis of PN before ART initiation. The Post-ART PN group included patients whose records showed a clinical diagnosis of PN after initiation of ART.

Ethics approval
The Kenyatta National Hospital / University of Nairobi-Ethics Research Committee approved the study protocol and all study subjects gave written informed consent on confidential use of information extracted from their medical records. and χ² tests respectively.

Results
After exclusion of patients with complete lack of laboratory data during the ART initiation, patients with duplicate data sets, and unconfirmed symptoms for polyneuropathy (PN), 320 patients (n=212 without PN, n=14 pre-ART PN, n=94 post-ART PN) were identified (Table 1).
Patients who developed PN during treatment did not differ at baseline in terms of gender, height, body mass index (BMI), CD4 count, ha emoglobin, white blood cell count, platelet count, CD4/CD8 ratio, initial ART (except TDF), time to first change of ART regime and ART duration overall from patients without PN over the course of the study. Patients with PN were older than the ones that did not develop PN. There was a significant difference in first-line ART regimen, with more patients on TDF based ART in the PN after treatment group. The study found no difference in other components of the first-line ART regime (Table 1). In

Discussion
The current retrospective cohort study that aimed at excluding height as an independent risk factor of PN found out that PN was a common disorder in HIV-infected Kenyan sex workers. These findings confirmed that PN is independently associated with increasing age but not height as postulated. The study also reports a significant difference in first-line ART regimen with more patients on TDF in the post-ART group. Although more patients were using d4T (48.4%) at baseline, there was no significant difference between patients who received d4T and controls. Although d4T is strongly associated with PN, these findings failed to confirm this association. Further, many patients previously not exposed to d4T ended up developing PN. Therefore, PN will remain a burden even with the rapid scale-up of ART that has so far transformed HIVinfection from a terminal illness to a chronic disease [29].
PN is a disabling neurological complication known to impair the quality of life of HIV-infected populations [30,31]. It is widely under- In the current analysis, age at baseline was significantly different in patients who developed PN versus controls. These findings support many previous studies that identified age as a risk factor for developing PN in HIV [2,5,20,36,37]. According to some authors, long, large and metabolically stressed peripheral nerves are likely particularly vulnerable to toxicity and damage caused by D-drugs [2]. So far, age stands out as the most notable and consistent risk factor for PN. With increased global access to ART and the rapidly aging HIV population on successful therapy, the association of aging as a risk factor in PN portends an ongoing burden from this complication for HIV therapeutics [2].
These results do not confirm the clinical impression that PN in HIV is length-dependent. However, a number of recent studies have associated patient height and risk of developing PN [2,[19][20][21][22][23].
According to these authors, taller patients are vulnerable to PN when exposed to d4T. The pathogenesis of the relation between height and PN remains conflicting. Some authors relate increased nerve length with greater axon surface area. They have suggested that any localized injury to an axon may impair the overall conduction properties of the nerve [24]. Therefore, patients with longer nerves (and thus a larger total axon surface area) may be at an increased risk of PN when exposed d4T [24]. In addition, greater leg length might relate to a prolonged time required to complete regeneration of any injured nerves. Alternatively, increased height could also relate to increased hydrostatic pressure experienced in the feet of tall patients when they stand up [38].
In almost all populations, height is significantly associated with gender, as the average female is smaller than the average male.
However, even when gender is controlled, height remains a controversial independent risk factor. Unlike studies that found height as an independent risk factor in HIV-PN, several other studies reported no association. For instance, two Rwandese studies found no association between height and PN [39,40]. Studies where gender was not controlled have produced controversial findings too.
Mehta et al. showed that the incidence of PN during the first year of ART was 10 times higher in woman than in men [22]. Since increased height is associated with male patients, one would expect a high incidence of PN in male than female patients. Exposure to "D drugs" including d4T has proved to be the most consistent risk factor associated with PN [7,9,41,42]. However, this study did not find a similar association. Other studies that reported no association between d4T and PN include studies by Luma et al., [31] and Tumusiime et al., [39]. Lack of association was suggested to be due to the limited proportion of d4T users or other risk factors other than d4T [35,43]. Further, the current findings suggest that the contradictory results observed in the above-mentioned studies, Page number not for citation purposes 5 may be due to a confounder that is associated with height and PN, such as alterations in metabolites or genetic variance.
The present study excluded known risk factors for PN other than HIV-associated PN and matched patients for gender and ART duration. After adjusting for those factors, the postulated association of height and the development of PN remained undetected. More than 50% of the patients who developed PN in this cohort never had any d4T exposure. Moreover, d4T exposed patients largely did not develop PN. Even after excluding known risk factors for PN, a number of patients still developed PN. These findings support other studies that have reported the ongoing high prevalence of PN in the absence of d4T exposure [30,33,[44][45][46].
For example, in a diverse cohort of more than 1 500 HIV-infected patients, more than half of the patients had PN [30]. Compared to earlier studies [33,[44][45][46], the prevalence of PN was not lower in this cohort even in the absence of d4T [30]. Before combination ART (cART), risk factors of PN included advancing age, immunosuppression, ongoing D-drug use, and elevated plasma HIVviral load [47,48]. These findings concurs with Ellis et al., that ongoing "D-drug" use is no longer associated with increased risk of PN [30]. Current CART use and previous D-drug exposure constitute new risk factors [30]. Moreover, the current findings reveal that even without exposure to d4T, some patients still develop PN. This suggests that unknown risk factors such as metabolites [43]

What this study adds
 Polyneuropathy is a more common disorder in resourcepoor settings (sex workers outreach programme health facilities);  Some patients still develop polyneuropathy even when they are not exposed to offending drugs including stavudine;  Older age is increasingly becoming an important a risk factor in aging patients on long-term ART.
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