Manganese poisoning

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Manganese Poisoning: Clinical Manifestations, Biochemical Changes, and Neuropathology

Introduction to Manganese Poisoning

Manganese poisoning, also known as manganism, is a condition resulting from chronic exposure to manganese (Mn), a metal commonly used in various industrial processes. This condition primarily affects the nervous system, leading to symptoms that often resemble Parkinson's disease .

Clinical Manifestations of Manganese Poisoning

Neurological and Psychiatric Symptoms

Chronic manganese poisoning presents with a range of neurological and psychiatric symptoms. These include motor disturbances such as tremors, muscle rigidity, and bradykinesia, as well as psychiatric symptoms like euphoria, emotional incontinence, and sleep disturbances . The most severe cases can lead to a "mask-like" facial expression, monotonous speech, and significant motor impairment .

Biochemical Changes

Biochemical studies have shown that manganese poisoning can lead to significant changes in serum calcium and adenosine deaminase levels. Mild and moderate poisoning cases exhibit increased serum calcium, while severe cases show a twofold increase in serum calcium and a threefold increase in adenosine deaminase levels. These biochemical markers can be crucial for early detection and diagnosis of manganese poisoning.

Mechanisms of Neurotoxicity

Oxidative Stress and Dopamine Depletion

Manganese ions, particularly in their trivalent form (Mn3+), can induce oxidative stress by oxidizing catecholamines such as dopamine, epinephrine, and norepinephrine. This oxidative process leads to a significant drop in dopamine levels, contributing to the neurological symptoms observed in manganese poisoning. The efficiency of Mn3+ in oxidizing these neurotransmitters under physiological conditions underscores its role in the neurotoxicity associated with manganese exposure.

Genetic Susceptibility

Recent studies have identified specific genes that may influence an individual's susceptibility to manganese poisoning. Genes involved in oxidative stress mechanisms, dopamine synthesis, and neuronal survival during apoptosis have been highlighted as potential factors affecting susceptibility. This genetic predisposition could explain the variability in clinical outcomes among individuals exposed to similar levels of manganese.

Neuropathological Findings

Brain Regions Affected

Autopsy studies of individuals with chronic manganese poisoning have revealed significant neuropathological changes, particularly in the basal ganglia. The pallidum, a part of the basal ganglia, shows severe degeneration, including loss of nerve cells and decreased myelinated fibers. Interestingly, the substantia nigra, another critical brain region involved in motor control, remains largely unaffected, differentiating manganese poisoning from Parkinson's disease.

Manganese Distribution in the Brain

Despite the severe neurological symptoms, studies have shown that the average concentration of manganese in the brain does not significantly differ between individuals with chronic manganese poisoning and control subjects. However, changes in the distribution of manganese within the brain have been observed, suggesting that the persistence of neurological symptoms is not directly linked to elevated manganese levels but rather to its distribution and the resulting localized neurotoxicity.

Conclusion

Manganese poisoning is a complex condition with significant neurological and psychiatric manifestations. The disease is characterized by biochemical changes, oxidative stress, and specific neuropathological alterations. Understanding the mechanisms of manganese neurotoxicity and the genetic factors influencing susceptibility can aid in the early detection, diagnosis, and management of this occupational hazard. Further research is needed to develop effective treatments and preventive measures for those at risk of manganese exposure.