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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.

Epidemiology

ALS typically is diagnosed in middle age. There is a recognised male predilection 1. The majority of cases are sporadic although a small proportion of cases are are thought to carry an autosomal dominant mutation on chromosome 21.

Clinical presentation

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 progressive loss of motor strength, with preservation of intellectual and sensory function. 

Pathology

ALS is a relentlessly progressive neurological disorder characterised by death of upper motor neurons (Betz cells in the cortex) and anterior horn cells with secondary Wallerian degeneration 2.

Radiographic features

MRI

The earliest MR manifestation is hyper intensity on T2WI in the corticospinal tracts, seen earliest in the internal capsule, as the fibers are most concentrated here. Eventually the entire tract from motor strip to the spinal cord is affected with increased T2 signal and volume loss 3

Iron deposition in the cortex is demonstrated as loss of signal, most evident on T2* weighted sequences (see Case 2 : SWI) - it is seen on T2WI in 40 - 60% (SWI is presumably more sensitive).

It is important to note that both of these features are present in varying degrees in normal control patients, and as such an appreciation what what is 'too much' is essential if MRI is to be of benefit. 

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.


Related articles

Neurodegenerative diseases

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. 

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