Etiology of OM

Although the pathophysiology of oral mucositis (OM) is not yet fully understood, recent clinical investigations have advanced our understanding of its origin and development. Historically OM was thought to be limited to the epithelial tissues of the oral cavity linings.1 These cells divide rapidly and were thought to be damaged along with targeted cancer cells during chemotherapy and/or radiotherapy therapy.2 Animal studies, however, showed that damage to the tissues beneath the surface began about a week before the lining showed signs of disease.2

Stephen T. Sonis D.M.D., D.M.Sc. (Division of Oral Medicine, Brigham and Women’s Hospital) divides OM development into five phases:

• Initiation
• Message generation
• Signaling and amplification
• Ulceration
• Healing3

Initiation occurs at the point of administration of chemotherapy or radiation therapy. Cells throughout the mouth’s tissues are damaged, and the damage creates proteins and other biological agents that generate biochemical messages and signals that contribute to further damage. It is important to understand that although all the events that ultimately lead to ulceration have begun at this point, the damage is focused on the submucosa and epithelium while the oral mucosa may still appear normal. Examining the patient’s mouth at this point will not necessarily reveal the ulceration that is about to occur.3

Ulceration occurs when the mucosal linings rupture. This is not only painful, but it also allows microbes to infiltrate the deep tissues. Once microbes begin to colonize, the infection may exacerbate the OM.2 Immunosuppressed patients are most susceptible to this outcome which may lead to infection and potentially fatal sepsis.4

Ultimately, healing begins as mucosal cells are nurtured by other cells and prompted to proceed toward renewal. Although the mucosa appears normal after healing, OM has had long-lasting effects on cells and tissues throughout the mucosa. The patient is more likely to develop OM again in future therapy.1

Chemotherapy and radiation therapy can cause OM. Because chemotherapy is administered in shorter intervals, the OM it causes typically occurs quickly and acutely. OM resulting from radiation therapy typically is more chronic and occurs over the longer period reflected by the therapy delivery schedule.3 Read about the Consequences of Oral Mucositis in this section.