Final answer:
The deficiency of thiamin characterized by symptoms such as loss of appetite, weight loss, and muscle weakness is called Beriberi, which can occur in several forms and has serious impacts on the nervous and cardiovascular systems.
Step-by-step explanation:
A thiamin deficiency characterized by loss of appetite, weight loss, confusion, muscle weakness, peripheral neuropathy is known as Beriberi. This condition is due to impaired utilization of carbohydrates, leading to an accumulation of pyruvate and lactate in cells, and is especially harmful to brain cells. Beriberi can present in various forms such as Dry Beriberi, where nervous system symptoms predominate, and Wet Beriberi, which includes edema and cardiovascular symptoms. There are also acute conditions like Wernicke's encephalopathy, typically seen in alcoholics, and infantile Beriberi, which affects breastfed infants whose mothers are thiamine deficient. In contrast, pellagra is the deficiency disease of niacin with symptoms of dermatitis, diarrhea, and dementia, while scurvy is due to a deficiency in vitamin C, leading to fragile capillaries and poor wound healing.