Facioscapulohumeral muscular dystrophy or FSHD is the most widespread of the nine primary types of muscular dystrophy affecting children and adults. Muscular dystrophy usually evokes a genetic, hereditary muscle that causes progressive muscular weakness. FSHD is also widely characterized as a neuromuscular disorder (NMD), such as muscular dystrophy is a subset of NMD. Muscular dystrophies are similar in that they cause progressive skeletal muscle weakness, defects in the biochemical components, physical and structural muscle and muscle cell death and tissue. However, researchers believe that the causes of each of the muscular dystrophies are not necessarily the same.
The major symptom of FSHD is the progressive weakening and loss of skeletal muscle. The usual location of these weaknesses at onset is the origin of the name: face (facio), shoulder girdle (scapula) and upper arms (humeral). Early weakness of the muscles of the eye (open and close) and mouth (smile, contraction, whistle) stand for FSHD. These symptoms, combined with weaknesses in the muscles that stabilize the scapular (shoulder blades) are often the basis of the doctor’s diagnosis of FSHD.
In most cases, FSHD muscle involvement begins in the face and slowly progressing to the shoulder and arm muscles, then to the abdominal muscles and foot extensors. Foot drop and foot weakness are early manifestations. First signs of FSHD include difficulty reaching above shoulder level, drop, improvise and scapular weakness of the face of the foot. Weakness in the abdominal muscles can cause a protuberant abdomen and lumbar lordosis. The lower abdominal muscles are generally weaker than the upper abdominal muscles. The distribution of weakness is not seen in many other diseases and, therefore, is very specific to FSHD.
Although the progression of FSHD is quite variable, it is usually relatively slow. With FSHD, most affected people develop unbalanced weaknesses (coast to coast). The reason for this asymmetry is unknown.
In more than half of FSHD cases, there are other symptoms, including a high frequency hearing loss or abnormal blood vessels behind the eye. Vascular anomalies in the back of the eye cause vision problems in only 1% of cases. Since these abnormalities are not exclusive to FSHD, we must keep in mind that their presence alone, to a person at risk for FSHD, is not sufficient for a diagnosis of FSHD.