Knuckle Pads

A clinical diagnosis, knuckle pads are benign well-circumscribed smooth, firm papules, nodules, or plaques. They typically are asymptomatic and overlie the joints on the dorsal hands; the thumbs and toes are less often involved. The name knuckle pad would seem to be a misnomer because in most reported cases, lesions occur over the proximal interphalangeal (PIP) joints rather than over the metacarpophalangeal (MCP) joints, better known as the knuckles.

Garrod first described knuckle pads in the medical literature in 1893.[1] However, knuckle pads have been observed since the Renaissance era; Michelangelo's statue of David demonstrates knuckle pads (Florence, Italy) as do his statues of Moses (Rome, Italy), Victory (Florence, Italy), and Giuliano de Medici (Rome, Italy).[2]

Knuckle pads may be idiopathic or inherited as part of autosomal dominant conditions such as Bart-Pumphrey syndrome and Dupuytren contracture. Similar to calluses, acquired forms are often a response to repetitive trauma and friction; many authors designate these lesions pseudo-knuckle pads.[3]

Knuckle pads may be idiopathic; however, they are often of the pseudo-knuckle pad variety and related to repetitive trauma . Predisoposing work-related trauma with repeated motions or rubbing of the PIP joints or knuckles, as seen in live-chicken hangers in a poultry processing plant,[4] has been reported. Athletes, such as boxers, have been known to traumatize their knuckles and fingers in a repetitive fashion, causing knuckle pads.[5, 6] Surfers have developed "surfer's knots" from repeated friction between the surfboard and the body part exposed to the repeated trauma.[7] A few cases involving the toes have been reported; these cases were thought to be sequelae of ill-fitting shoes.

Psychologically disturbed children who bite and suck their fingers cause thickenings that resemble knuckle pads to occur in the skin in the traumatized areas. Patients with bulimia who use their knuckles or fingers to induce emesis sometimes develop fibrotic papules resembling knuckle pads.[8]

Some cases of knuckle pads are familial. They have been associated with autosomal dominant palmoplantar keratoderma with and without ichthyosis vulgaris. Knuckle pads were also found in two families with autosomal dominant sensorineural deafness and leukonychia (Bart-Pumphrey syndrome).[9] They have also been reported in pseudoxanthoma elasticum.[10, 11, 12]

Dupuytren disease, Peyronie disease, and Ledderhose disease are at times observed together, and the triad may be associated with knuckle pads.[13, 14, 15] The presence of knuckle pads in the setting of Dupuytren disease has been shown to predict a high genetic risk for Dupuytren diathesis.[16] Of interest, one research group studying Dupuytren disease sought to differentiate dorsal cutaneous pads, typical knuckle pads, from subcutaneous solid tumor–like masses overlying the digital joints coined dorsal Dupuytren nodules. In their study, the prevalence of typical knuckle pads was similar in patients with Dupuytren disease and the healthy population. However, the deeper subcutaneous nodules, dorsal Dupuytren nodules, were found only in the setting of Dupuytren disease.[17]

Knuckle pads have been associated with esophageal cancer,[18] hyperkeratosis,[19] oral leukoplakia,[18] pachyonychia congenita,[20] and clubbed fingers.[21] One case report links phenytoin with polyfibromatosis syndrome.[22] Idiopathic familial association has been described in one case report.[23]

In one study of patients with knuckle pads compared with an age- and sex-matched control group, the frequency of metabolic syndrome was similar, but compared with the control group, more patients with knuckle pads had hypertension and abdominal obesity. A role for insulin resistance and resultant hyperinsulinemia triggering insulinlike growth factor to stimulate keratinocyte and fibroblast proliferation was suggested.[24]

Frequency

Knuckle pads are a common occurrence. Measurement of knuckle pad prevalence is difficult as patients typically are asymptomatic and do not seek medical attention for them. In one epidemiologic study in Norway, roughly 9% of 1871 individuals without Dupuytren disease had knuckle pads; in the study group with Dupuytren disease, the incidence of knuckle pads was much higher.[14]

Race

No racial predilection is associated with knuckle pads.

Sex

In the same Norwegian study group of persons without Dupuytren disease, the incidence of knuckle pads was the same for men and women. However, in the group with Dupuytren disease, 48.7% of men and 33.3% of women had associated knuckle pads.[14]

The sex-based prevalence of trauma-induced pseudo-knuckle pads may depend on the predisposing activity. For example, occupation-associated knuckle pads (pseudo-knuckle pads) have been reported more commonly in the dominant hand of men with more physically demanding occupations.[17]

Age

Knuckle pads can present at any age. They have been reported in young children who bite and suck their fingers.[25] More commonly, knuckle pads are observed in adults older than 40 years.[14]

Little morbidity is associated with knuckle pads as they typically are asymptomatic. Some patients may experience pain and difficulty with hand functioning, including writing, as a result of their condition. Cosmetic issues drive most patients to seek attention for knuckle pads. Spontaneous resolution can occur, especially if an inciting repetitive injury is identified and eliminated. In most cases, knuckle pads persist indefinitely with little change.

Firm, skin-colored papules appear sequentially in multiple sites typically overlying the PIP but also the distal interphalangeal (DIP) and/or MCP joints of the hands. Dorsal toes are occasionally involved. Individual lesions enlarge into well-defined plaques and nodules. Complaints of pain and functional impairment of fine motor skills are rare. Cosmetic concerns may be raised. A history of repetitive trauma is often elicited.

Knuckle pads are well-circumscribed firm dermal papules, nodules, or plaques approximately 0.5-3 cm in size, located on the extensor aspect of the joints of the hands and occasionally on the toes. Lesions may be bilateral, but typically are not symmetrical. If subjected to repetitive injury, knuckle pads may develop over virtually any bony prominence, but the PIP joint area is most commonly affected. See the images below.

Knuckle pad over the proximal interphalangeal joint.

Multiple knuckle pads on various joints of the hand.

Laboratory studies are not helpful in establishing the diagnosis of knuckle pads.

A biopsy is indicated if the diagnosis is in doubt.

The histology of knuckle pads shows changes in both the epidermis and dermis. Epidermal abnormalities include hyperkeratosis and acanthosis. During the proliferative phase, plumb fibroblasts within loose bands of collagen form an unencapsulated dermal nodule. The fibrotic stage is less cellular, with spindle-shaped fibroblasts and thickened, irregular collagen bundles.[29] In the case of the dorsal nodules of Dupuytren disease, the pathologic findings are similar to those seen in the palmar nodules characteristic of this diathesis.[17]

Neither medical nor surgical interventions for knuckle pads are very effective. Eliminating the source of mechanical or repetitive trauma may improve the lesions. Wearing protective gloves or changing occupation may be necessary. Intralesional injections of corticosteroids or fluorouracil may reduce the size of the lesions.[3] Lesions caused by biting or sucking may require a psychiatrist to treat the underlying psychological problem. A cast or splint placed temporarily on the involved areas of the hand may aid in reducing the lesion. Application of silicone gel sheeting has had limited success.[30] Applications of keratolytics, such as salicylic acid or urea, have helped to soften and even reduce the lesions. Radiation therapy and application of solid carbon dioxide have been reported to be of some help in selected cases.

Surgical intervention may be indicated if knuckle pads cause a functional problem. Recurrence after surgery is likely, especially if the trauma that caused the initial knuckle pad is not eliminated. Scar or keloid formation may result from surgical intervention. Tendon tethering, another surgical complication, occurs only if the joint space or capsule is accidentally cut with damage to the tendon in the attempt to remove the knuckle pad.[31]

Complications of knuckle pads occur if surgery is used to remove the lesion. Complications include scar or keloid formation, recurrence, or tendon tethering (see Surgical Care). Most knuckle pads are asymptomatic and require no treatment.

The goals of pharmacotherapy are to reduce morbidity and prevent complications.

Class Summary

Keratolytics cause cornified epithelium to swell, soften, macerate, and then desquamate.

Salicylic acid topical (Dr. Scholl' s)

By dissolving the intercellular cement substance, topical salicylic acid produces desquamation of the horny layer of skin, while not affecting structure of viable epidermis.

Urea (Ureacin, Ureaphil, Carmol)

Urea promotes hydration and removal of excess keratin in conditions of hyperkeratosis. It is available in 10-50% concentrations.