The temporalis muscle is a broad, fan-shaped muscle located on the side of the head, occupying the temporal fossa above the cheekbone. It is one of the four muscles of mastication, primarily functioning to elevate the mandible, or lower jaw, to close the mouth and assist in jaw retraction. Temporal muscle wasting (TMW) is a localized loss of muscle mass, or atrophy, in this area. TMW is not a disease itself, but a physical sign indicating an underlying systemic or localized health problem causing muscle tissue breakdown.
Recognizing Temporal Muscle Wasting
The physical signs of temporal muscle wasting are visible on the sides of the head near the temples. A healthy temporalis muscle gives the area a smooth, full, or slightly convex contour. When atrophy occurs, this fullness is lost, and the area takes on a depressed or hollowed appearance.
This volume loss in the temple region is often one of the most noticeable features of the condition. As the muscle shrinks, the underlying bone structures become more prominent and defined. Specifically, the temporal crest and the zygomatic arch, or cheekbone, may appear starkly visible beneath the skin.
The degree of concavity can be assessed visually, sometimes categorized into grades based on the depth of the depression relative to the eyebrow. In unilateral cases, where only one side is affected, the asymmetry between the two sides of the face is pronounced. Healthcare professionals may palpate the area while the patient clenches their jaw to manually assess the muscle’s size and strength compared to the unaffected side.
Primary Causes of Temporal Muscle Atrophy
The causes of temporal muscle atrophy are broadly divided into systemic issues affecting the entire body and localized issues specific to the head and neck. TMW often indicates a severe, body-wide energy deficit, as the body breaks down muscle tissue for energy when nutrient intake is inadequate.
Systemic Causes
Severe malnutrition is a primary systemic cause, resulting from a prolonged lack of adequate calories, protein, and other nutrients that leads to generalized muscle wasting. A more accelerated and profound form is cachexia, a complex metabolic syndrome associated with chronic diseases. Cachexia is often seen in advanced cases of cancer, chronic obstructive pulmonary disease (COPD), heart failure, and acquired immunodeficiency syndrome (AIDS).
TMW in these conditions is a clear indicator of a high catabolic state, where breakdown processes far exceed the body’s ability to build new tissue. Advanced aging also contributes through sarcopenia, the progressive, age-related loss of skeletal muscle mass and strength. The thinning of the temporalis muscle can be one of the earliest recognizable signs of sarcopenia.
Neurological and Localized Causes
Atrophy can occur due to issues preventing the temporalis muscle from being used or receiving proper nerve signals. The muscle is controlled by the mandibular branch of the trigeminal nerve (CN V). Damage or compression of this nerve can lead to a type of wasting called denervation atrophy.
When nerve signaling is interrupted, muscle fibers rapidly shrink because they are no longer stimulated to contract. Conditions such as tumors pressing on the trigeminal nerve or localized inflammatory disorders, like masticatory muscle myositis, can cause this atrophy. This form of wasting is often unilateral, affecting only the muscle on the damaged side.
Strategies for Addressing and Managing Muscle Wasting
Successful management of temporal muscle wasting relies on identifying and treating the underlying disease or condition. The visible atrophy will only reverse once the systemic or localized cause has been effectively managed. Management is typically multidisciplinary, combining nutritional support with physical rehabilitation.
Nutritional Intervention
Addressing the nutritional deficit is paramount, especially in cases related to malnutrition or cachexia. This requires a high-calorie, high-protein diet to provide the necessary building blocks for muscle repair and growth. Increased protein intake supplies the amino acids needed to reverse the catabolic state.
Medical nutritional supplements, often liquid, may deliver concentrated nutrients to patients who have difficulty eating or absorbing food. In severe cases, or when swallowing is compromised, tube feeding may be implemented to ensure consistent, high-density caloric and protein intake. Treating the underlying disease, such as stabilizing a chronic infection or managing an active malignancy, reduces the systemic inflammation that drives muscle breakdown.
Physical and Rehabilitative Therapy
Physical therapy plays a supportive but significant role in recovery by promoting the return of function and muscle strength. Specific exercises are used for the muscles of mastication to encourage movement, range of motion, and coordinated contraction. These can include resisted mouth opening, where light pressure is applied against the jaw as the mouth opens, to strengthen the temporalis and other jaw-closing muscles.
Other exercises, such as controlled jaw movements like “goldfish exercises” or side-to-side glides, help re-establish proper function and coordination. While these exercises are often used for jaw joint disorders, they are adapted to stimulate and strengthen the weakened temporalis muscle fibers. Combining targeted resistance exercise with adequate nutritional fuel is the most effective approach for rebuilding lost muscle mass.