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The thenar region of the palm refers to the group of muscles in the thick pad just underneath the thumb. Thenar atrophy is an eroding of muscle tissue, which can impair control over the thumb and leave the hand disfigured. The problem can be a complication of several different conditions and disorders, including carpal tunnel syndrome, acromegaly, or direct trauma to the wrist or thumb. In addition, atrophy can occur if the wrist and hand are immobilized in a cast for several weeks or months. Treatment measures are usually focused on curing or managing the underlying cause and gradually rebuilding strength through guided physical therapy.
Three muscles, several tendons, and a small area of protective cartilage tissue are found in the thenar region. The muscle group that controls the movement of the thumb is stimulated by a long, vital structure called the median nerve. Most cases of atrophy have to due with problems related to the median nerve. When it is compressed or severed, the resulting lapse of electrical activity in the hand means that the muscles are never exercised; unstimulated muscle tissue wastes away over time.
Advanced carpal tunnel syndrome is the most common cause of thenar atrophy. Inflammation of the wrist joint caused by frequent overuse narrows the passageway of the median nerve, resulting in numbness, weakness, and chronic pain. Atrophy can occur in the late stages of carpal tunnel, which may cause partial or total paralysis of the region.
Acromegaly is a hormonal disorder that affects the way body tissues grow, including those in the wrist and thenar region. Overgrowth of bone tissue may put pressure on the median nerve and other nerve branches elsewhere in the body. Atrophy of the thenar region is a common complication of median nerve compression.
Prolonged immobilization is another potential cause of atrophy in patients who break their thumbs or wrists. The hard casts use to keep bones from moving can also impede muscle movement; as bones heal, unused muscles waste away.
Thenar atrophy due to any cause is usually very noticeable. There might be an obvious dent in the palm or along the outer edge of the base of the thumb. At rest, the thumb may be fixed in a rigid position across the front of the palm. In cases of severe atrophy, it is impossible to bend or move the thumb at all.
A medical professional can usually identify the cause of atrophy by asking about a patient's medical history and taking diagnostic imaging scans of the hand. Depending on the underlying condition, a patient may need to take specialized medications or undergo surgery to decompress the median nerve. Physical therapy is important in the recovery stages to safely and effectively rebuild muscle mass in the thenar region. A healthcare professional may also decide to schedule a clinical electro-stimulation procedure to massage and work the muscles. With treatment, most cases can be reversed.