The course of these diseases is relentlessly progressive, with increasing functional limitation over time. The functional limitations listed below are in order of emergence from early to late.

• Upper extremity mobility

• Strength

• Whole body mobility

• Self-care

• Speech

These disorders typically onset after the age of forty when most people are either competitively employed or engaged in homemaking. The initial symptoms involve weakness and reduced coordination and dexterity in the hands and feet. Whether these symptoms produce a vocational impediment at this point depends primarily on the requirements of the person's employment. Persons employed in agriculture, industrial, clerical, and homemaking occupations may encounter vocational problems very early in the course of the disease. Persons in professional, technical, managerial, and sales occupations are more likely to first encounter difficulties in self-care and activities of daily living. Since these conditions cannot be treated, however, one can expect this latter group to begin to encounter vocational problems soon afterward.

Since most persons are either employed or engaged in homemaking at the time of onset, the basic vocational rehabilitation strategy is one of maintaining current employment. This strategy is most readily achieved using rehabilitation engineering, job modification and restructuring, and assistive devices. Current employment in professional, technical, managerial, clerical, sales, and homemaking is a positive indicator of long-term employability potential because cognitive functions remain intact and physical demands can be altered with rehabilitation engineering approaches.

Retention of employment in agricultural and industrial occupations is more problematic because of the motor requirements involved. A thorough job and task analysis of current employment will usually disclose the extent to which a rehabilitation engineering approach can be applied. Close work with the employer will also indicate whether transfer into other jobs within the firm is possible, with or without some type of training.

Although it is tempting to consider rate of progress of the disease in determining long-term employability, this is pointless in everyday practice. There is no way to estimate this in an individual case, particularly when the person comes to vocational rehabilitation early in the course of the disease.