A case of knuckle pad syndrome in a middle‐aged man

Abstract

Knuckle pads are benign papules, nodules, or plaques overlying joints and typically manifest at the proximal interphalangeal joints (PIPs). They may be confused with other dermatologic or rheumatologic diseases. Treatment options for primary knuckle pads are limited and acquired knuckle pads typically improve with withdrawal of the offending insult.

Knuckle pads are uncommonly encountered in clinical practice and may be mistaken for other rheumatologic diseases. They are benign, typically manifest in early adulthood, and may be idiopathic, hereditary, or acquired. They have a distinct appearance on musculoskeletal ultrasound, which can be used to spare unnecessary further diagnostic evaluation.

1. CASE DESCRIPTION

A 58‐year‐old man presented for the evaluation of joint deformity of the bilateral hands for several years. His past medical history included cervical spine stenosis with myelopathy. There was no history of joint pain or joint swelling, but he did report morning stiffness lasting several hours. He reported that his hands feel tight and this sensation was worse with use. His review of systems was otherwise unrevealing including no fever, chills, night sweats, malaise, visual changes, rash, oral ulcers, hair loss, dry eyes, dry mouth, photosensitivity, Raynaud's phenomenon, chest pain, dyspnea, diarrhea, hematochezia, hematuria, back pain, symptoms suggestive of dactylitis, Achilles tendonitis, or plantar fasciitis. There was no history of similar lesions in family members or family history of rheumatologic disease. He was previously employed as a school teacher and has since retired.

Vital signs were normal. Physical examination revealed a healthy‐appearing middle‐aged male with multiple subcutaneous nodules of the bilateral hands at the PIPs and DIPs without evidence of synovitis as displayed in Figure 1. There were dystrophic nails. There was no skin rash.

FIGURE 1.

Image of the bilateral hands featuring multiple subcutaneous nodules overlying the PIPs and DIPs.

X‐rays of the bilateral hands were obtained as displayed in Figures 2 and 3. Studies were remarkable for moderate first carpometacarpal joint osteoarthritis of the right hand. Rheumatoid factor and cyclic citrullinated peptide antibodies were negative.

FIGURE 2.

Radiographs of the right hand.

FIGURE 3.

Radiograph of the left hand.

Musculoskeletal ultrasound of the right hand was performed to evaluate for synovitis. There was no evidence for synovitis, tenosynovitis, or erosions of the dorsal wrist. The carpal and volar recesses were unremarkable. There was mild osteophyte formation with grade 1 synovitis of MCP 2 on dorsal, volar, and side views. The third and fourth fingers were unremarkable for synovitis, tenosynovitis, or erosions on dorsal and volar views. Thickened dermis of the second (Figures 4 and 5), third (Figures 6 and 7), and fourth fingers was seen on dorsal view with otherwise unrevealing images including no synovitis, tenosynovitis, or erosions. There was no evidence of synovitis, tenosynovitis, or erosions on dorsal and volar views of the long DIP of the second, third, fourth, and fifth fingers.

FIGURE 4.

Right Long PIP of the 2nd finger with Doppler examination with thickened dermis superficially.

FIGURE 5.

Transverse PIP of the 2nd finger with Doppler examination with thickened dermis superficially.

FIGURE 6.

Right Long PIP of the 3rd finger with Doppler examination with thickened dermis superficially.

FIGURE 7.

Transverse PIP of the 3rd finger with Doppler examination with thickened dermis superficially.

Patient was diagnosed with idiopathic knuckle pads on the basis of clinical history and musculoskeletal ultrasound. He was provided reassurance about the benign nature of the findings.

2. CASE DISCUSSION

Knuckle pads are well‐circumscribed smooth, firm papules, nodules, or plaques overlying the small joints of the hands and feet. They were first described in 1893 by Garrod but have been observed in the works of the sculpturist Michelangelo dating back to the 1500s. ¹ They are benign fibromas and typically asymptomatic but may occasionally be painful. They typically present at the PIP joints rather than the MCP joints but can present in any of the small joints of the hands. ² Less commonly, the feet and knees may be involved.

The pathophysiology has not been entirely elucidated, and knuckle pads are typically idiopathic. They are a fibromatous disease with fibroblast proliferation that then develops into fibrosis. ³ They typically manifest in the second and third decades of life. ⁴ They may be seen in a number of inherited syndromes including palmar fibromatosis (Dupuytren's disease), plantar fibromatosis (Ledderhose's disease), camptodactyly, epidermolytic palmoplantar keratoderma, Bart–Pumphrey syndrome, and acrokeratoelastoidosis of Costa. ² , ⁵ , ⁶ , ⁷ They may also be secondary and acquired through trauma. Secondary knuckle pads are well‐described among athletes such as in boxers and swimmers as well as in certain professions such as carpet layers. ⁸ , ⁹ , ¹⁰ Knuckle pads have also been described in patients with bulimia nervosa and obsessive–compulsive disorder. ¹¹ , ¹² The histopathology of secondary knuckle pads is distinctly different from primary knuckle pads and demonstrates hyperkeratosis with hypergranulosis and acanthosis. ⁴ It is histologically similar to callus.

Due to the appearance of the lesions and close association with joints such as the PIP, it may be clinically difficult to distinguish knuckle pads from other entities such as synovitis, rheumatoid nodules, Heberden nodes, or even gouty arthropathy. Knuckle pads may also be difficult to distinguish from other dermatologic diagnoses such as erythema elevatum diutinum, verruca, granuloma annulare, and pachydermodactyly. ¹³ , ¹⁴ , ¹⁵ , ¹⁶ Patients are often referred to rheumatologists for evaluation and undergo evaluation for rheumatologic disease such as in the case of our patient. Distinguishing knuckle pads from synovitis may be challenging on the basis of physical examination alone. Musculoskeletal ultrasound may be helpful to characterize knuckle pads, which have a distinct appearance on ultrasound.

On ultrasound, primary knuckle pads will appear as subcutaneous hypoechogenic nodular thickenings. They typically have a dome shape with irregular borders and are noncompressible with the transducer. Power Doppler should be performed, which will reveal absent vascularization or only involvement of the periphery of the lesion. The adjacent soft tissue, tendons, and joints should not be involved. Rarely, MRI may be performed, which will demonstrate low‐to‐intermediate signal intensity on T1‐W1 and T2‐WI MRI. ⁴ , ¹⁷ , ¹⁸ , ¹⁹ , ²⁰

Treatment of knuckle pads may be challenging. They are benign, but some patients may desire intervention for cosmetic purposes in which case there are limited therapies. Some authors have described successful application of intralesional triamcinolone as well as fluorouracil, cantharidin‐podophyllotoxin‐salicylic acid, and topical high‐dose salicylic acid and urea. ²¹ , ²² , ²³ , ²⁴ Acquired knuckle pads such as in the case of repetitive trauma should improve within months if the offending insult is removed.

3. CONCLUSIONS

Knuckle pads are a rare, benign clinical entity and can be classified according to whether they are primary or secondary. They may be difficult to distinguish clinically from other rheumatologic processes such as synovitis, early psoriatic arthritis, or rheumatoid nodules. Musculoskeletal ultrasound may be helpful in establishing the diagnosis. The clinical course is benign, and therapeutic interventions are limited.

AUTHOR CONTRIBUTIONS

Zachary Chandler: Conceptualization; writing – original draft; writing – review and editing. Kimberly Seamon: Conceptualization; writing – original draft; writing – review and editing. Karishma Ramsubeik: Conceptualization; investigation; resources; supervision. Gurjit Kaeley: Conceptualization; data curation; software; supervision; visualization.

FUNDING INFORMATION

The author(s) received no financial support for the research, authorship, and/or publication of this article.

CONFLICT OF INTEREST

The authors whose names are listed above certify that they have NO affiliations with or involvement in any organization or entity with any financial interest or nonfinancial interest in the subject matter or materials discussed in this manuscript.

ETHICAL APPROVAL

An ethics approval was not required in our case due to reported data being part of the evaluation of patient and no patient interventions performed.

CONSENT

Written consent was obtained from the patient to publish his case.

Chandler Z, Seamon K, Ramsubeik K, Kaeley G. A case of knuckle pad syndrome in a middle‐aged man. Clin Case Rep. 2022;10:e06740. doi: 10.1002/ccr3.6740

DATA AVAILABILITY STATEMENT

The original contributions presented in the case report are included in the article/supplementary material; further inquiries can be directed to the corresponding author/s. Deidentified data is available on request.