Knuckle pads, also known as

heloderma ''Heloderma'' is a genus of toxicoferan lizards that contains five species, all of which are venomous. It is the only extant genus of the family Helodermatidae. Description The genus ''Heloderma'' contains the Gila monster (''H. suspectum'') a ...

, meaning similar to the skin of the

Gila monster The Gila monster (''Heloderma suspectum'', ) is a species of venomous lizard native to the Southwestern United States and the northwestern Mexico, Mexican state of Sonora. It is a heavy, slow-moving reptile, up to long, and it is the only ve ...

lizard for which it is named, are circumscribed, keratotic, fibrous growths over the

dorsa Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position provi ...

of the interphalangeal joints. They are described as well-defined, round, plaque-like, fibrous thickening that may develop at any age, and grow to be 10 to 15mm in diameter in the course of a few weeks or months, then go away over time. Knuckle pads are sometimes associated with Dupuytren's contracture and

camptodactyly Camptodactyly is a medical condition that causes one or more Digit (anatomy), digits (fingers or toes) to be permanently bent. It involves fixed Human anatomical terms#Types of movement, flexion deformity of the proximal interphalangeal articulat ...

, and histologically, the lesions are

fibroma Fibromas are benign tumors that are composed of fibrous or connective tissue. They can grow in all organs, arising from mesenchyme tissue. The term "fibroblastic" or "fibromatous" is used to describe tumors of the fibrous connective tissue. Wh ...

s. Knuckle pads are generally non-responsive to treatment, including

corticosteroid Corticosteroids are a class of steroid hormones that are produced in the adrenal cortex of vertebrates, as well as the synthetic analogues of these hormones. Two main classes of corticosteroids, glucocorticoids and mineralocorticoids, are invo ...

s, and tend to recur after surgery; however, there has been some effectiveness with intralesional

fluorouracil Fluorouracil (5-FU, 5-fluorouracil), sold under the brand name Adrucil among others, is a cytotoxic chemotherapy medication used to treat cancer. By intravenous injection it is used for treatment of colorectal cancer, oesophageal cancer, stoma ...

Signs and symptoms

Knuckle pads are benign subcutaneous fibrotic nodules that are seen in the finger joints and/or the extensor area of the foot. From a clinical perspective, these are well-defined, non-compressible, freely moveable lesions that resemble

warts Warts are non-cancerous viral growths usually occurring on the hands and feet but which can also affect other locations, such as the genitals or face. One or many warts may appear. They are distinguished from cancerous tumors as they are caus ...

and primarily affect the dorsal portion of the proximal interphalangeal (PIP) and, less frequently, the

metacarpophalangeal The metacarpophalangeal joints (MCP) are situated between the metacarpal bones and the proximal phalanges of the fingers. These joints are of the condyloid kind, formed by the reception of the rounded heads of the metacarpal bones into shallow ...

(MCP) joints. Knuckle pads are often asymptomatic, painless, and progressive in their growth, reaching their final size of up to 40 mm in diameter. They also do not cause any functional impact on the joints, such as decreased flexibility or altered

tendons A tendon or sinew is a tough band of dense fibrous connective tissue that connects muscle to bone. It sends the mechanical forces of muscle contraction to the skeletal system, while withstanding tension. Tendons, like ligaments, are made of ...

Causes

Since the pathogenesis is yet unclear, knuckle pads are usually

idiopathic An idiopathic disease is any disease with an unknown cause or mechanism of apparent spontaneous origin. For some medical conditions, one or more causes are somewhat understood, but in a certain percentage of people with the condition, the cause ...

. They are a fibromatous illness characterized by

fibroblast A fibroblast is a type of cell (biology), biological cell typically with a spindle shape that synthesizes the extracellular matrix and collagen, produces the structural framework (Stroma (tissue), stroma) for animal Tissue (biology), tissues, and ...

growth leading to

fibrosis Fibrosis, also known as fibrotic scarring, is the development of fibrous connective tissue in response to an injury. Fibrosis can be a normal connective tissue deposition or excessive tissue deposition caused by a disease. Repeated injuries, ch ...

. Acrokeratoelastoidosis of Costa,

, epidermolytic palmoplantar keratoderma, Dupuytren's disease, plantar fibromatosis ( Ledderhose's disease), and Bart-Pumphrey syndrome are among the hereditary syndromes in which knuckle pads may be observed. Knuckle pads can also be acquired subsequent to trauma. In sports like boxers and swimmers, as well as in some occupations like carpet layers, secondary knuckle pads are well-documented. Knuckle pads have also been reported in individuals suffering from obsessive-compulsive disorder and

bulimia nervosa Bulimia nervosa, also known simply as bulimia, is an eating disorder characterized by binge eating (eating large quantities of food in a short period of time, often feeling out of control) followed by compensatory behaviors, such as self-indu ...

Diagnosis

The diagnosis of knuckle pads is clinical. The differential diagnosis includes retained foreign objects,

neurofibromas A neurofibroma is a benign nerve-sheath tumor in the peripheral nervous system. In 90% of cases, they are found as stand-alone tumors (solitary neurofibroma, solitary nerve sheath tumor or sporadic neurofibroma), while the remainder are found in ...

, rheumatoid nodules, gouty tophi,

xanthomas A xanthoma (pl. xanthomas or xanthomata) (condition: xanthomatosis) is a deposition of yellowish cholesterol-rich material that can appear anywhere in the body in various disease states. They are cutaneous manifestations of lipidosis in which lip ...

, synovial cysts, and Bouchards and Heberdens nodes. When a diagnosis is unclear, plain

radiographs Radiography is an imaging technique using X-rays, gamma rays, or similar ionizing radiation and non-ionizing radiation to view the internal form of an object. Applications of radiography include medical ("diagnostic" radiography and "therapeu ...

histology Histology, also known as microscopic anatomy or microanatomy, is the branch of biology that studies the microscopic anatomy of biological tissue (biology), tissues. Histology is the microscopic counterpart to gross anatomy, which looks at large ...

(if

sonography Medical ultrasound includes diagnostic techniques (mainly imaging) using ultrasound, as well as therapeutic applications of ultrasound. In diagnosis, it is used to create an image of internal body structures such as tendons, muscles, joints ...

is not conclusive), and

ultrasound Ultrasound is sound with frequency, frequencies greater than 20 Hertz, kilohertz. This frequency is the approximate upper audible hearing range, limit of human hearing in healthy young adults. The physical principles of acoustic waves apply ...

improve the information-gathering process and lower the possibility of a misdiagnosis. Knuckle pads show up as noncompressible, dome-shaped, hypoechoic

nodules Nodule may refer to: *Nodule (geology), a small rock or mineral cluster *Manganese nodule, a metallic concretion found on the seafloor *Nodule (medicine), a small aggregation of cells *Root nodule Root nodules are found on the roots of plants, p ...

ultrasonography Medical ultrasound includes diagnostic techniques (mainly imaging) using ultrasound, as well as therapeutic applications of ultrasound. In diagnosis, it is used to create an image of internal body structures such as tendons, muscles, joints, ...

and as peripheral or nonexistent vascularization on

Doppler The Doppler effect (also Doppler shift) is the change in the frequency of a wave in relation to an observer who is moving relative to the source of the wave. The ''Doppler effect'' is named after the physicist Christian Doppler, who described ...

analysis. On

, the pads show enhanced proliferation of (myo-)

fibroblasts A fibroblast is a type of biological cell typically with a spindle shape that synthesizes the extracellular matrix and collagen, produces the structural framework ( stroma) for animal tissues, and plays a critical role in wound healing. Fibrobla ...

, which is frequently linked to

hyperkeratosis Hyperkeratosis is thickening of the stratum corneum (the outermost layer of the epidermis, or skin), often associated with the presence of an abnormal quantity of keratin,Kumar, Vinay; Fausto, Nelso; Abbas, Abul (2004) ''Robbins & Cotran Pathol ...

Treatment

In the lack of targeted and efficacious treatments, a stressful wait-and-see strategy is typically advised. Surgery has also been utilized, though typically without producing a change in appearance. Potential adverse effects include

scars SCARS or S.C.A.R.S. is an acronym that may refer to: * SCARS (military) (Special Combat Aggressive Reactionary System), an American combat fighting system * Severe cutaneous adverse reactions Severe cutaneous adverse reactions (SCARs) are a gr ...

keloids Keloid, also known as keloid disorder and keloidal scar, is the formation of a type of scar which, depending on its maturity, is composed mainly of either type III (early) or type I (late) collagen. It is a result of an overgrowth of granulation t ...

, post-operative loss of joint flexibility, and recurrences. A small number of treatments have shown promise recently, but they are frequently moderately to highly invasive and are primarily based on case reports. Intralesional

triamcinolone Triamcinolone is a glucocorticoid used to treat certain skin diseases, allergies, and rheumatic disorders among others. It is also used to prevent worsening of asthma and chronic obstructive pulmonary disease (COPD). It can be taken in variou ...

cantharidin Cantharidin is an odorless, colorless fatty substance of the terpenoid class, which is secreted by many species of blister beetles. Its main current use in pharmacology is treating molluscum contagiosum and warts topically. It is a burn agent ...

podophyllotoxin Podophyllotoxin (PPT) is the active ingredient in Podofilox, a medical cream used to treat genital warts and molluscum contagiosum. It is not recommended for HPV infections without external warts. It can be applied either by a healthcare provi ...

salicylic acid Salicylic acid is an organic compound with the formula HOC6H4COOH. A colorless (or white), bitter-tasting solid, it is a precursor to and a active metabolite, metabolite of acetylsalicylic acid (aspirin). It is a plant hormone, and has been lis ...

, and topical high-dose

and

urea Urea, also called carbamide (because it is a diamide of carbonic acid), is an organic compound with chemical formula . This amide has two Amine, amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest am ...

have all been successfully applied, according to certain authors. If the knuckle pads are caused by repetitive trauma, they should heal in a couple of months after the trauma ceases.

References

External links

DermNet

Cleveland Clinic
{{Soft tissue disorders Dermal and subcutaneous growths Soft tissue disorders