CNS causes are brain tumour,aneurysm,hormonal disturbances,diabetes,multiple sclerosis,
zinc deficiency, malnutrition etc.Loss of taste sensation can be due to nasal infections,flu,common cold, dryness of mouth, medications like antithyroid medications,rifampicin,gingivitis,vitamin B12 or zinc deficiency. You should consult a primary care physician. Based on your clinical examination findings he may further refer you to the concerned specialist. Treatment will depend on the underlying cause.