As the name indicates, this form mainly involves the upper extremities. It appears in some cases to have an autosomal recessive inheritance pattern. This disorder starts later in life (second to the fifth decades), and the disease is often so benign that years may elapse before it is diagnosed. Weakness is generally asymmetric and may spare the deltoid, supraspinatus, and infraspinatus muscles. Not until very late in life may the lower extremities show signs of involvement. The progression of the disease is very slow, and patients have a normal life expectancy. The disability experienced by patients is fairly minimal, although frozen shoulder syndrome may significantly alter function if it is bilateral. Intellectual deterioration and cardiac involvement are rare.
Muscle weakness is first evident in the shoulder girdle and later in the pelvic girdle. Early onset is infrequent; the disease course is variable, but usually milder than that in the pelvofemoral phenotype.
Physical therapy and stretching exercises can prevent contractures and muscle atrophy and thus help to slow disease progression.