**4. Clinical manifestations of neurotoxicity**

These manifestations include signs and symptoms in multiple parts of the central nervous system, including the central, peripheral, and autonomic nervous systems and skeletal muscle. They are typically accompanied by discomfort, altered sensations, such as taste and smell, decreased visual acuity, and hearing loss [5, 6].

#### **4.1 Encephalopathy**

Acute encephalopathies are a common occurrence. The majority are insignificant and dissipate within a few days. Headache, weariness, disorientation, loss of attention and short-term memory, lack of motor coordination, and the resulting gait irregularity, nausea, and dizziness are the most common indications and symptoms. Schaumburg identified several compounds (about 100) as possible causative factors, including aluminum, cannabis, cocaine, domoic acid, lead, organic solvents, and trimethyltin. While acute symptoms commonly resolve rapidly, chronic issues can significantly debilitating influence on job performance and productivity. There is a significant need for long-term follow-up and mental and psychological disorders assessment. Acute (moderate) encephalopathy rarely progresses to chronic (severe) encephalopathy with progressive cognitive and psychomotor impairment [5–7].

#### **4.2 Movement disturbance**

Cerebellar dysfunction, manifested by ataxia, intention tremor, and lack of coordination, is well documented due to chronic mercury exposure; however, overdose with various potentially lethal medications and substances, including 5-fluorouracil, lithium, and acrylamide, has also been reported. Cerebellar dysfunction is notoriously challenging to diagnose. Extrapyramidal syndromes such as parkinsonism, dystonias, dyskinesias, and tics are relatively well-defined toxic syndromes. While the destructive processes are unknown, they are frequently reversible, although symptoms can return years after the condition begins. Parkinsonism is arguably the most well-known form of Parkinson's disease, owing to an epidemic involving people exposed to MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine), a contaminant found in certain illicit substances. Most syndromes are induced by excessive medication use, particularly phenothiazines, rather than by exposure to non-therapeutic drugs [6–9].
