Amyotrophic lateral sclerosis
Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig disease or Charcot disease, is the most common form of motor neuron disease 1,4 resulting in progressive weakness and eventual death.
ALS typically is diagnosed in middle age. There is a recognised male predilection 1.
Both upper and lower motor neurons are affected with decreased motor strength and with wasting of the muscles of the face, limbs and diaphragm. There is a progressive loss of motor strength, with preservation of intellectual and sensory function.
El Escorial criteria for the diagnosis of amyotrophic lateral sclerosis 7:
- it requires the presence of
- signs of lower motor neuron (LMN) degeneration by clinical, electrophysiological or neuropathologic examination
- signs of upper motor neuron (UMN) degeneration by clinical examination
- progressive spread of signs within a region or to other regions
- together with the absence of
- electrophysiological evidence of other disease processes that might explain the signs of LMN and/or UMN degenerations
- neuroimaging evidence of other disease processes that might explain the observed clinical and electrophysiological signs
The majority of cases are sporadic and thus less well understood. In the familial form of ALS several genes mutations have been identified (e.g. SOD1, TDP-43, FUS and the hexanucleotide repeat expansion in C9ORF72) 5.
The earliest MR manifestation is hyperintensity on T2WI in the corticospinal tracts, seen earliest in the internal capsule, as the fibres are most concentrated here. Eventually, the entire tract from motor strip to the spinal cord is affected by increased T2 signal and volume loss 3.
Iron deposition in the cortex is demonstrated as loss of signal, most evident on T2* weighted sequences, it is seen on T2WI in ~50%.
It is important to note that both of these features are present in varying degrees in normal control patients, and as such an appreciation of what is too much is essential if MRI is to be of benefit.
- T2: hyperintensity in the corticospinal tracts (specificity <70% and sensitivity <40%) 6
MR spectroscopy 2
- decreased NAA
- decreased glutamate
- increased choline
- increased myoinositol
Treatment and prognosis
ALS typically progresses to death in 2-6 years, usually from respiratory complications 5.
Neurodegenerative diseases are legion and their classification just as protean. A useful approach is to divide them according to underlying pathological process, although even using this schema, there is much overlap and thus resulting confusion.
neurodegenerative MRI brain (an approach)
- measurements and ratios
- midbrain to pons area ratio (for PSP)
- Magnetic Resonance Parkinsonism Index (MRPI) (for PSP)
- frontal horn width to intercaudate distance ratio (FH/CC) (for Huntington disease)
- intercaudate distance to inner table width ratio (CC/IT) (for Huntington disease)
- scoring systems
- measurements and ratios
- typical/classical Alzheimer disease
- variant (e.g. posterior cortical atrophy)
- chronic traumatic encephalopathy (CTE)
- corticobasal degeneration
- frontotemporal lobar degeneration (FTLD) (not all are tau)
- Pick disease
- progressive supranuclear palsy (PSP)
- Alzheimer disease
- cerebral amyloidosis
- spinocerebellar ataxias
- Huntington disease
- hereditary spastic paraplegia
- amyotrophic lateral sclerosis (ALS)
- clinically unclassifiable parkinsonism (CUP)
- Unverricht-Lundborg disease
- prion diseases (not always included as neurodegenerative)
- 1. Khader SM, Greiner FG. Neuroradiology case of the day. Amyotrophic lateral sclerosis. Radiographics. 19 (6): 1696-8. Radiographics (full text) - Pubmed citation
- 2. Chan S, Shungu DC, Douglas-Akinwande A et-al. Motor neuron diseases: comparison of single-voxel proton MR spectroscopy of the motor cortex with MR imaging of the brain. Radiology. 1999;212 (3): 763-9. Radiology (full text) - Pubmed citation
- 3. Cheung G, Gawel MJ, Cooper PW et-al. Amyotrophic lateral sclerosis: correlation of clinical and MR imaging findings. Radiology. 1995;194 (1): 263-70. Radiology (abstract) - Pubmed citation
- 4. Nelles M, Block W, Träber F et-al. Combined 3T diffusion tensor tractography and 1H-MR spectroscopy in motor neuron disease. AJNR Am J Neuroradiol. 2008;29 (9): 1708-14. doi:10.3174/ajnr.A1201 - Pubmed citation
- 5. Traynor BJ, Cleveland DW. Special Issue on amyotrophic lateral sclerosis. Exp. Neurol. 2014;262 Pt B: 73-4. doi:10.1016/j.expneurol.2014.08.020 - Free text at pubmed - Pubmed citation
- 6. Simon NG, Turner MR, Vucic S et-al. Quantifying disease progression in amyotrophic lateral sclerosis. Ann. Neurol. 2014;76 (5): 643-57. doi:10.1002/ana.24273 - Free text at pubmed - Pubmed citation
- 7. Brooks BR. El Escorial World Federation of Neurology criteria for the diagnosis of amyotrophic lateral sclerosis. Subcommittee on Motor Neuron Diseases/Amyotrophic Lateral Sclerosis of the World Federation of Neurology Research Group on Neuromuscular Diseases and the El Escorial "Clinical limits of amyotrophic lateral sclerosis" workshop contributors. J. Neurol. Sci. 1995;124 Suppl: 96-107. Pubmed citation