Introduction:
Mesoamerican nephropathy (MeN) is a chronic disease of the kidney affecting young agricultural workers of Central America. The cause of this condition is not known. This condition was first described in 1999-2000 when many individuals were initiated on dialysis. A high prevalence of chronic kidney disease with unknown etiology was found in regions of El Salvador, Nicaragua, Guatemala, Costa Rica, and Mexico.
What Is a Mesoamerican Nephropathy?
The chronic disease of unknown etiology among Pacific Coast of Central America individuals. This condition is an epidemic disease (the disease occurring widely in a community at a particular period). It majorly affects men working outdoors. The main group affected is sugarcane workers.
This condition has been present since 1970, and a marked increase has been seen during the past two decades. More than 20,000 deaths have been documented because of the non-availability of dialysis to everyone affected with Mesoamerican nephropathy.
The condition is mainly seen among outdoor workers, especially sugarcane workers, construction workers, subsistence farmers, and other similar groups. This condition is now seen in other countries like India, Bangladesh, Sri Lanka, Egypt, Mexico, and Central America.
What Is the Role of Dehydration as a Cause of Mesoamerican Nephropathy?
One of the important characteristics of all the groups of people affected by Mesoamerican nephropathy is dehydration, which occurs during heavy work in a hot environment. This disease is more common among workers who work in sugarcane fields that are situated at lower altitudes when compared to those who work in fields that are situated at higher altitudes.
According to studies conducted, it was found that the workers continue to work in the heat indexes that cross unsafe zones. The Occupational Safety and Health Administration defines a hazardous zone. Many workers develop signs of dehydration that include fainting, lightheadedness, and jittery. Heat stroke is always confused with fever; dysuria can be seen frequently; urine analysis shows concentrated urine (increased specific gravity and elevated urine osmolarity) at the end of the day. This occurs cyclically daily.
Historically, it was thought that dehydration (loss of water) and volume depletion (loss of salt) may result in pre-renal disease. In this kind of condition, no actual damage or injury is present unless there is a drop in blood pressure and renal blood flow. This drop in blood pressure and renal blood flow may lead to acute tubular necrosis.
A study conducted among mice showed that recurrent dehydration associated with exposure to heat developed impaired renal function and tubulointerstitial fibrosis. Another finding of this study is about the timing of the hydration given to mice. The hydration given after each dehydration cycle was more beneficial when compared to hydration given at the end of the day. This finding was helpful to know about the timing of hydration. When this finding was correlated with sugarcane workers, it was found that hydration to those workers should be given while working in the field, which is more beneficial when compared to hydration if given at the end of the day.
A study showed why the kidney gets injured. The study was done and observed on mice. They found that the mice lost salt and water through sweat on their feet and became hyperosmolar during the day. This change activated the kidney's proximal tubule of the kidney, which activated the enzyme system (aldose-reductase-sorbitol dehydrogenase-fructokinase).
This enzyme system acts by converting glucose being reabsorbed in the proximal tubule into fructose. This fructose is then metabolized to produce oxidants and uric acid by the fructokinase enzyme. The oxidants and uric acid produced are responsible for causing local tubular injury. Another interesting point was that the mice without fructokinase enzyme but were exposed to dehydration did not have kidney injury and were protected from kidney damage.
What Are the New Insights Into Kidney Injury?
New Insights about kidney injury caused by Mesoamerican Nephropathy were found. The mechanism behind this was an exercise done under heat stress was found to cause subclinical rhabdomyolysis. This rhabdomyolysis is associated with the release of nucleotides and a rise in serum uric acid.
Hyperuricemia is most commonly seen among sugarcane workers. The serum uric acid also increases during the daytime. Hence, the dehydration that occurs during the daytime results in urinary concentration and acidification. This, again, results in high urinary uric acid concentrations that can exceed the solubility. Urinary crystals can be commonly seen among sugarcane workers when urine sedimentation is done. It was found that sugarcane workers develop urine uric acid levels greater than 100mg/dl daily. This concentration is similar to the urine uric acid levels found in individuals suffering from acute kidney injury following chemotherapy. Hence, it was proposed that Mesoamerican nephropathy may be caused due to repeated episodes of hyperuricosuria and urate crystal formation. These formations occur due to hard work on hot days with limited or delayed hydration.
Why Mesoamerican Nephropathy Is an Epidemic?
There has been a rise in temperature in the last century. This temperature rise has led to increased hot days. A study has found that 75% of extremely hot days are due to global warming. Workers working on such hot days, especially sugarcane workers working in the fields, are exposed to heat, and the intensity of their work adds to and increases their body's core temperature.
Mesoamerican nephropathy is not confined to Central America but is seen in many other countries. Hence, it was understood that chronic kidney disease might be common among those working outside, exposed to sunshine, and frequently in areas with a water shortage or scarcity of potable water.
Finally, Mesoamerican nephropathy is associated with global warming that is caused due to the extensive use of fossil fuels and the greenhouse effect.
How to Diagnose Mesoamerican Nephropathy?
It is challenging to identify this condition. The following tests may provide the diagnosis.
If suspected disease,
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Estimated GFR (eGFR) < 60 ml/min/1,73m2
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The absence of diabetes, hypertension, autoimmune diseases, etc., is an apparent cause of the disease.
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Residing in the hot region.
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Proteinuria < 2g/24h or 2g/g urine creatinine.
If the disease is likely, all the tests mentioned above should be performed.
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eGFR < 60 ml/min/1,73m2 for three months or longer repeat measurement.
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Relative hyperkalemia or hyperuricemia.
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Kidney ultrasound.
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Kidney biopsy.
What Is the Treatment of Mesoamerican Nephropathy?
No standard treatment is available, and the treatment options adopted by healthcare providers may vary.
As there is no specific treatment, the condition can be improved by
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Accessing shade.
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Hydration.
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Rest.
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Access to clean air and water.
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Avoiding nephrotoxic substances.
Conclusion:
Mesoamerican nephropathy is a condition of unknown cause. This condition mainly affects those working in hot weather conditions without proper hydration. This condition is characterized by chronic kidney disease. Hence, knowing about this condition, why it occurs, and how to diagnose and treat it is important. Knowing about the condition helps to take precautionary measures to avoid the disease.
