Diagnostic criteria

There is presently no diagnostic marker for ALS, and therefore the diagnosis of this disease depends upon the recognition of a characteristic clinical constellation of symptoms and signs with supportive electro-physiological findings. An additional requirement for the diagnosis of ALS is the exclusion of other disorders which may have similar clinical features. The constellation of weakness and muscle wasting which crosses both a peripheral nerve and myotomal distribution, and is associated with fasciculations and hyper-reflexia, is nearly always due to ALS. From the point of view of therapy, it would be ideal to be able to identify cases of ALS in a pre-symptomatic phase before neural death has occurred. It is probable that by the time clinical deficits appear and the diagnosis is more evident, the possibility of reversing the progression of the disease is less feasible. Diagnosis of ALS during the pre-symptomatic period must await the identification of a biochemical or other biological marker for ALS with proven specificity and sensitivity that has been assessed in prospective studies.

Once the disease has been present for a few months, the diagnosis of ALS can usually be made with a reasonable degree of confidence and is normally straightforward. The combination of painless, progressive but asymmetrical muscle weakness with wasting, fasciculation (and cramps), associated with upper motoneuron signs, a normal sensory examination, and normal sphincter and ocular function in a middle-aged patient is almost always due to ALS. As an additional support for the diagnosis, it is necessary to exclude other causes for the symptoms, especially those producing a cervical cord syndrome.