Introduction
Neurodegenerative diseases include a very wide group of disorders affecting the central nervous system (CNS). Many of these disorders arise from the combined effects of genetic predisposition and environmental factors.
This results in reduced cognition (e.g. Alzheimer’s disease, dementia with Lewy bodies, and vascular dementia), motor system performance (e.g. amyotrophic lateral sclerosis), or both (e.g. Parkinson’s disease and prion diseases). In general, neurodegenerative diseases show a wide diversity of etiology and a broad clinical phenotype spectrum, but all have in common the
decrease in neuronal function and neuronal cell death due to activation of apoptotic pathways, programmed cell death, or other mechanisms.

The evolution of magnetic resonance (MR) techniques for imaging the CNS has led to significant advances in the understanding of brain changes associated with neurodegenerative disorders. Conventional MR imaging (MRI) provides detailed anatomic information with excellent tissue contrast and spatial resolution. Additional MR sequences can provide information concerning tissue metabolism, water diffusion, and perfusion. All together, these MR modalities have been demonstrated to be relevant in the clinical evaluation of neurodegenerative disorders for early diagnosis, differential diagnosis, and monitoring of disease activity. MR spectroscopy (MRS), in particular, has provided insights into some of the metabolic abnormalities associated with neurodegeneration, thereby helping to elucidate the underlying pathophysiology of these disorders, although it has yet to have significant impact in routine clinical usage. The goal here is to describe the common findings of MR spectroscopy (MRS) in this field and its limitations. We will focus on proton MRS (1H-MRS), as the majority of MRS studies in neurodegenerative disorders utilize this technique and it can readily be performed as part of a routine MR study. It should be stressed, however, that other nuclei (such as 31P or 13C) have been used in research studies of various neurodegenerative disorders.

Dementia
Dementia is a clinical diagnosis defined as a decline in memory and other cognitive functions that affect the daily life in an alert patient. Major causes of dementia include Alzheimer’s disease (AD) and vascular dementia (VD) and, less commonly, frontotemporal dementia and dementia with Lewy bodies. Consensus clinical criteria have been applied for diagnosis of different dementias, but the sensitivity and specificity of these criteria are variable. The diagnosis of dementing disorders by means of the current clinical criteria remains difficult and, occasionally, due to the mixed pathology existing in the brain of demented patients, the underlying cause of dementia cannot be definitely determined even after the histopathologic examination of the brain.
The difficulty in making diagnoses exclusively based on the current clinical criteria has generated the incentive for identifying specific neuroimaging markers for various dementing pathologies. Thus, in vivo changes of demented brains have been studied with different MR modalities with increasing frequency.
In this context, 1H-MRS has been shown to be useful in the differential diagnosis of dementing illnesses, as well as in monitoring early disease progression and effectiveness of therapies.

Fig.1 Clinical features of dementia. This figure shows some of the common features of dementia that are caused by degenerative changes in different parts of the cerebral cortex (frontal lobe = red, parietal lobe = blue, temporal lobe = yellow). The clinical picture in a particular person depends upon the distribution and severity of the changes. From Paul Jones-Clinical Neuroscience.