The exact number of people living with Thoracic Outlet Syndrome (TOS) is difficult to determine, making its true prevalence a topic of discussion. TOS refers to a group of disorders caused by the compression of nerves or blood vessels within the thoracic outlet—the confined space between the collarbone and the first rib. While the condition is relatively uncommon, the varying nature of its subtypes and diagnostic challenges suggest that official statistics may underrepresent the number of affected individuals.
Defining Thoracic Outlet Syndrome (TOS)
The thoracic outlet is a narrow anatomical passageway at the lower neck and upper chest. It serves as a transit point for the neurovascular bundle supplying the arm, which includes the brachial plexus nerves, the subclavian artery, and the subclavian vein. When surrounding structures—such as the scalene muscles, the clavicle, or the first rib—impinge upon these nerves or vessels, TOS symptoms develop.
Compression is often triggered by changes in the space’s dimensions due to anatomical variations or external factors. Some individuals are born with predisposing features, such as a cervical rib (an extra rib) or an abnormally elongated process of the seventh cervical vertebra. More commonly, the syndrome is initiated by trauma, like a whiplash injury, or by repetitive strain from activities involving sustained arm movements. These factors lead to mechanical pressure or tension on the nerves and vessels, resulting in symptoms like pain, numbness, tingling, or weakness in the neck, shoulder, arm, or hand.
The Major Subtypes of TOS
The prevalence figures for Thoracic Outlet Syndrome differ dramatically depending on which of its three primary classifications is discussed. The syndrome is categorized based on the specific structure that is compressed.
Neurogenic Thoracic Outlet Syndrome (NTOS) is the most frequent type, accounting for an estimated 90% to 97% of all TOS cases. This form involves the compression of the brachial plexus, the network of nerves controlling movement and sensation in the arm and hand. Symptoms are neurological, including pain and a “pins and needles” sensation, often worsening with overhead activities. Women are more frequently affected by NTOS than men, sometimes reporting a ratio as high as 3.5 to 1.
The two vascular types, Venous TOS (VTOS) and Arterial TOS (ATOS), are much less common. VTOS results from compression of the subclavian vein, usually leading to symptoms like swelling, heaviness, and a bluish discoloration of the arm. This compression can sometimes cause a blood clot, a condition known as Paget-Schroetter syndrome. VTOS is estimated to represent about 2% to 5% of cases.
Arterial TOS is the least common but potentially most serious form, involving the compression or injury of the subclavian artery. This type is primarily associated with congenital bony abnormalities, such as a cervical rib. Symptoms arise from reduced blood flow, presenting as coldness, paleness, or non-healing sores in the fingers. ATOS accounts for the smallest fraction of cases, often cited as less than 1%.
Challenges in Determining True Prevalence
Establishing a definitive measure of TOS prevalence remains a significant challenge for researchers and clinicians. A primary reason for this ambiguity is the difficulty in diagnosing Neurogenic TOS (NTOS), the most prevalent subtype. NTOS symptoms—pain, numbness, and tingling—overlap substantially with those of far more common conditions, such as carpal tunnel syndrome, cervical disc herniation, and rotator cuff problems.
This overlap often leads to misdiagnosis or underreporting, as patients are treated for other conditions without recognizing the underlying nerve compression. Compounding the issue is the lack of a single, objective, and universally accepted diagnostic test for NTOS. Unlike the vascular types, which can be confirmed with objective imaging like ultrasound or CT angiography, NTOS diagnosis relies heavily on a clinical evaluation, including a patient’s history and provocative physical maneuvers that reproduce symptoms.
The subjective nature of the symptoms and the reliance on clinical judgment, rather than a clear biological marker, make it difficult to collect consistent data across different medical centers and research studies. This variability in diagnostic criteria contributes to the wide range of prevalence estimates reported in medical literature. The question of “how common” is thus inseparable from the debate over diagnostic standards.
Reported Frequency and Affected Populations
Despite the diagnostic challenges, available medical data offer some estimates for the annual incidence of TOS. The vascular forms are considered rare. The estimated yearly incidence for Venous TOS (VTOS) is around one case per 100,000 people, with Arterial TOS (ATOS) being even less frequent.
The frequency of Neurogenic TOS (NTOS) is subject to wider speculation. However, recent estimates from specialized centers suggest an annual incidence of approximately three cases per 100,000 people. Since NTOS accounts for the vast majority of cases, the overall incidence of TOS is often quoted as being in the range of 2.5 to 4 cases per 100,000 people per year.
The syndrome demonstrates clear demographic patterns, particularly for the neurogenic type. Women are significantly more likely to be diagnosed with NTOS, often presenting between their 20s and 40s. All types of TOS are disproportionately found in individuals whose work or athletic activities involve repetitive overhead arm motions, such as swimmers, baseball pitchers, and manual laborers. The combination of a congenital predisposition and an acquired factor, like trauma or repetitive strain, places these populations at higher risk.