Russell’s sign is a distinctive physical finding characterized by calluses, abrasions, or scarring on the back of the hand, typically over the metacarpophalangeal and interphalangeal joints. Named after British psychiatrist Gerald Russell, who first described it in 1979, the sign is an important dermatological manifestation in a specific clinical context. Its presence suggests a history of a specific compensatory behavior often hidden from clinicians and family members.
The Physical Characteristics and Cause
The physical manifestation of Russell’s sign is concentrated on the dorsal surface of the hand, typically involving the index and middle fingers of the dominant hand. These areas develop thickened, rough skin (hyperkeratosis), presenting as a callus. Lesions may also appear as fresh abrasions, small lacerations, or scarred areas, sometimes accompanied by hyperpigmentation, or darkening of the skin. Severity ranges from subtle roughness to pronounced, discolored scarring, depending on the behavior’s duration and frequency.
The cause of this localized skin damage is direct, repeated mechanical trauma against the teeth. The sign develops when an individual repeatedly inserts fingers into their mouth and throat to trigger the gag reflex and induce vomiting. As the fingers are forced down, the knuckles repeatedly contact the incisor teeth. This friction and scraping action leads to the formation of scar tissue and protective calluses over time.
Diagnostic Importance of the Sign
The medical significance of Russell’s sign lies in its powerful association with self-induced vomiting (purging), a behavior seen in certain eating disorders. While not everyone who purges develops this sign, its presence is a strong clinical indicator suggesting an underlying eating disorder, most commonly Bulimia Nervosa (BN). It can also be seen in the purging subtype of Anorexia Nervosa or other specified feeding or eating disorders.
For clinicians, Russell’s sign is a valuable, observable clue to a behavior that is often secretive and denied. Because BN does not necessarily involve the extreme weight loss seen in anorexia, this physical sign can be one of the few pieces of objective evidence available for diagnosis. Identifying this subtle physical marker helps healthcare professionals initiate a comprehensive assessment, including patient history and psychiatric evaluation. Early recognition facilitates timely intervention and treatment for the underlying mental health condition.
Other Potential Causes of Knuckle Markings
Not all markings on the knuckles constitute Russell’s sign, as similar-looking calluses can arise from various forms of repetitive friction. These “pseudo-knuckle pads” are callosities caused by chronic localized trauma unrelated to purging. For example, individuals in manual occupations, such as carpet layers or tailors, may develop calluses due to constant rubbing against surfaces.
Sports involving repetitive impact, such as martial arts like boxing, can also cause abrasions or thickening over the knuckles. Additionally, a variety of dermatological conditions and genetic disorders, including Dupuytren’s contracture and pachydermodactyly, can result in thickened knuckle skin. Clinicians differentiate Russell’s sign from these other causes by considering the specific location of the lesions, the patient’s medical history, and the presence of other associated physical symptoms of eating disorders, such as dental erosion.
What Happens to the Sign During Recovery
Once the purging behavior ceases, the physical manifestations of Russell’s sign begin to heal as the traumatic friction stops. Any fresh abrasions or lacerations will close and resolve relatively quickly, like any other skin injury.
However, calluses and scar tissue developed over a long period may take an extended time to diminish, or they may not disappear at all. If the self-induced vomiting was chronic, the skin may have undergone permanent changes, resulting in residual hyperpigmentation or noticeable scarring. Healing the physical sign is secondary to treating the underlying eating disorder, as the skin changes only resolve with sustained behavioral recovery.