An 11-year-old girl presented with a 4-year history of asymptomatic plaques over her knuckles. She denied trauma to the affected areas. Her review of systems including fatigue, muscle weakness, or sun sensitivity revealed no abnormalities. Past medical history and family history were unremarkable. She was treated with emollients and over-the-counter strength hydrocortisone without any improvement in the appearance or thickness of the plaques. Physical examination revealed hyperkeratotic lichenified erythematous and hypopigmented plaques over the proximal interphalangeal joints of all 10 fingers. She had no involvement of the toes, no palmoplantar keratoderma, and no nailfold telangiectasia. A skin biopsy specimen was obtained from a lesion on the right index finger. Histopathologic examination of the skin section showed hyperkeratosis and acanthosis without signs of inflammation.
Figure 1 . Photograph shows hyperkeratotic plaques over the proximal interphalangeal joints of all 10 fingers.
Knuckle pads were first reported in the medical literature by Garrod in 1893.1 Knuckle pads are well-circumscribed, usually asymptomatic, hyperkeratotic plaques of the skin over the metacarpophalangeal and, more commonly, the proximal interphalangeal joints. They can occur at any age but are most frequently seen in teenagers and young adults.2 The incidence in children is not known, and there seem to be no gender or racial predispositions,3
Knuckle pads grow slowly throughout months to years and can range from a few millimeters to a few centimeters. They may be solitary or multiple and usually do not appear simultaneously but develop sequentially. They are freely movable over underlying joints and can be hypopigmented or hyperpigmented, particularly those who are in dark-skinned.2 They are rarely found on the toes.
Histologically, knuckle pads are either characterized by a marked acanthosis and a slight proliferation of fibroblasts and capillaries of the upper dermis without inflammatory cell infiltrate,4 or by predominantly dermal changes with marked fibroblast proliferation and thickened, irregular collagen bundles and a minimal epidermal hyperkeratosis.5
Although most cases of knuckle pads in children are idiopathic, inherited or acquired forms have also been reported. They have been described in association with inherited syndromes such as acrokeratoelastoidosis Costa,6 leukonychia, deafness with or without palmoplanar keratoderma,7,8 and knuckle pads with autosomal dominant palmoplanar keratoderma with or without ichthyosis vulgaris.2,9 Acquired knuckle pads in children have been associated with repetitive friction and trauma caused by obsessive-compulsive behavior or sports.10,2 In adults, the most common cause of knuckle pads is trauma related to occupational exposure.13 Several cases of knuckle pads in association with Dupuytren's disease, Ledderhose disease, and Peyronie's disease3 have been reported in adults.
The differential diagnose of knuckle pads includes calluses, Verrucae vulgaris, granuloma annulare, xanthomas, foreign body reactions, rheumatoid nodules, Gottron's papules, and scars.10
In the management of knuckle pads, it is important to exclude an underlying disease or a possible traumatic trigger that could be eliminated. The treatment of idiopathic knuckle pads is often ineffective and usually unnecessary.2 They have been reported to resolve spontaneously in children.13 In some cases, topical treatments with a potent corticosteroid under occlusion or with keratolytic agents such as lactic acid, salicylic acid, or urea have been successful. Intralesional corticosteroids have been used with some success, but this therapy is painful and inappropriate for young children.2 Excision of the knuckle pads should be avoided because the primary lesions often recur and the surgery may lead to severe scaring.
1. Garrod AE. On an unusual form of nodufe upon the joints of the fingers. St. Bartholomew's Hosp Rep. 1893;29:157-161.
2. Palier AS, Hebert AA. Knuckle pads in children. Am J Dis Child. 1986;140(9):915-917.
3. Mikkelsen OA. Knuckle pads in Dupuytren's disease. Hand. 1977;9(3):301-305.
4. Allison JR, Allison JR. Knuckle pads. Arch Dermatol. 1966;9(3):311-316.
5. Lagier R, Meinecke R. Pathology of "knuckle pads:" Study of four cases. Virehows Arch A Pathol Anat Histol. 1975,365(3): 185-191.
6. Cosa OG. Acrokerato elastoidosis. Dermatology. 1953;107:164-168.
7. Bart RS, Pumphrey RE. Knuckle pads, leukonychia, and deafness. N Engl J Med. 1967;276(4):202-207.
8. Crosby EF, Vidurrizaga RH. Knuckle pads, leukonychia, deafness and Keratosis palmoplantaris. Report of a family. Johns Hopkins Med J. 1976;139(Suppl):90-92.
9. Sehgal VN, Singh M, Saxena HMK, et al. Primary knuckle pads. Clin Exp Dermatol. 1979;4(3):337-339.
10. Peterson CM, Barnes CJ, Davis LS. Knuckle pads: does knuckle cracking play an etiologic role? Pediatr Derma toi. 2000;17(6):450-452.
11. Calikoglu E. Pseudo-knuckle pads: an unusual cutaneous sign of obsessive-compulsive disorder in an adolescent patient. Turk J Pediatr. 2003;45(4):348-349.
12. Dickens R, Adams BB, Mutasim DF. Sports-related pads, Int J Dermatol. 2002;41(5):29 1-293.
13. Mackey SL, Cobb MW. Knuckle pads. Cutis. 1994,54(3): 159-160.