Skin Disorders Guide

Diagnostic Hallmarks

1. Distribution: random but some predilection for the back
2. History of a preceding noninflammatory cyst or nodule
3. Solid fragments of white keratin on incision and drainage

Clinical Presentation

Asymptomatic, skin-colored epidermoid cysts occasionally become red and tender. When this occurs, differentiation from a furuncle may become difficult. The history of a preceding noninflammatory nodule, the absence of a pustule at the summit, and somewhat lesser pain suggest, however, a cystic process. Inflamed cysts can occur almost anywhere, but most are encountered on the trunk with special predilection for the back

Course and Prognosis

Inflamed cysts are generally accompanied by sufficient discomfort to bring the patient to medical attention. If left untreated, the inflammation generally resolves spontaneously over 2 to 4 weeks. A large, fluctuant inflamed cyst may rupture, however, with subsequent chronic drainage. Treated lesions are likely to recur unless the entire cyst wall has been successfully removed.

Pathogenesis

The inflammatory changes are rarely the result of true bacterial infection. They occur instead because of the extrusion of keratinous material (and, possibly, nonpathogenic follicular bacteria) through a ruptured cyst wall. Sometimes the rupture of the wall occurs as a result of trauma, but often it appears to occur spontaneously.

Therapy

Small lesions can be excised, but most lesions will first require incision and drainage. When this procedure is carried out, there is usually a larger-than-expected amount of purulent, foul-smelling material that can be expressed. Almost always, some pieces of solid, yellow-white keratin are mixed in with the fluid material. This contrasts with the situation in furunculosis wherein only a small amount of pure pus is present. A significant cavity is left when large cysts are incised and drained. Such “dead space” should be packed with gauze packing, the tail of which is left to extend through the incision site. Cultures can be taken from the expressed material, but they rarely demonstrate pathogenic bacteria. Systemically administered antibiotics are used routinely by some clinicians, but I doubt that they actually speed up the course of resolution. An attempt to remove all of the cyst wall through the incision site is worthwhile but is usually not successful. I prefer to let the process heal completely over a 2-month period and then consider elliptical excision of the small papule that remains.