Pectoralis minor syndrome (PMS) is a condition related to thoracic outlet syndrome (TOS) that results from the

pectoralis minor Pectoralis minor muscle () is a thin, triangular muscle, situated at the upper part of the chest, beneath the pectoralis major in the human body. Structure Attachments Pectoralis minor muscle arises from the upper margins and outer surfaces ...

muscle being too tight. PMS results from the

brachial plexus The brachial plexus is a network () of nerves formed by the anterior rami of the lower four cervical nerves and first thoracic nerve ( C5, C6, C7, C8, and T1). This plexus extends from the spinal cord, through the cervicoaxillary canal in th ...

being compressed under the pectoralis minor while TOS involves compression of the bundle above the

clavicle The clavicle, or collarbone, is a slender, S-shaped long bone approximately 6 inches (15 cm) long that serves as a strut between the shoulder blade and the sternum (breastbone). There are two clavicles, one on the left and one on the rig ...

. In most patients, the nerves are constricted resulting in neurogenic PMS, but venous compression (venous PMS) can also occur. PMS and TOS often, but not always, occur together. They share similar symptoms including tingling, pain, or weakness in the hand and arm, but in PMS there is also pain or tenderness in the

chest wall The thoracic wall or chest wall is the boundary of the thoracic cavity. Structure The bone, bony human skeleton, skeletal part of the thoracic wall is the rib cage, and the rest is made up of muscle, skin, and fasciae. The chest wall has 10 lay ...

where the pectoralis minor attaches to the scapula as well as in the armpit. One study of 100 patients diagnosed with neurogenic TOS found that 75 percent also had neurogenic PMS and 30 percent in fact had PMS without TOS. PMS is often caused by injury to the neck, excessive stretching of the shoulder, or certain sports that involve overhead throwing. Confirmation of the diagnosis can be done by blocking the pectoralis minor muscle or injecting botulinium. First-line treatment for patients with PMS but without TOS is self-stretching of the pectoralis minor muscle. Other treatments include injection of botulinium, or surgery that cuts the pectoralis minor tendon. For patients with PMS but without TOS, one study found that surgery resulted in a good or excellent outcome in 90 percent of cases. Another study in ten patients with PMS substantially resolved symptoms in all but one case. PMS was first described in 1945.

References

Further reading