FSHD is characterized by progressive weakness and atrophy of the face, shoulder girdle, and upper arm muscles. Muscle weakness most often manifests itself around 20, but it can be present in infancy or later in adulthood.
The most common initial symptom is the inability to raise the arms above shoulders. In addition, the weakening of the facial muscles generates problems with making a smile, whistling, or drinking through a straw. Over time, there is also extensive involvement of the leg muscles. This is especially true of the early stages of the tibialis anterior and gastrocnemius muscles. As a result, feet drop is present frequently as the disease progresses.
In FSHD, there may also be pronounced involvement of the abdominal muscles and paraspinal muscles. This poses a risk of developing lumbar lordosis or camptocormia (bending the lower back forward). About 10% of all patients and 20% of people over the age of 50 will eventually lose their ability to move independently.
The pattern of muscle weakness is usually asymmetric, and the rate and degree of progression can vary widely (even within related patients). The right shoulder and arm muscles are more often affected by atrophy than the left side. The deltoid muscle is usually spared, which is a hallmark of FSHD. This is not the case in any other shoulder girdle dystrophy. Sometimes the disease progresses quickly and in an unexplained manner. Contrary to other muscular dystrophies, contractures around weak muscles are not commonly observed. The reason why specific muscle groups are used and others are saved has not yet been established.
In addition to muscle damage, the course of the disease may also lead to progressive damage to hearing. This phenomenon is described in about 16% of patients, and often it concerns selectively high-frequency sounds and may proceed unnoticed. Additionally, in the course of FSHD, changes in the structure of blood vessels present in the back of the eyeball are found. Such changes are observed in about 50-75% of patients. Mostly the course is also asymptomatic.
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