TITLE: A Case of Knuckle Pad Syndrome in a Middle-Aged Man
Zachary Chandler, DO, Resident, Division of General Medicine, Department
of Medicine, UF COM - Jacksonville, Jacksonville, FL.
Zachary.Chandler@jax.ufl.edu
Kimberly Seamon, MD, Resident, Division of General Medicine, Department
of Medicine, UF COM - Jacksonville, Jacksonville, FL.
Kimberly.Seamon@jax.ufl.edu
Karishma Ramsubeik, MBBS, Attending Physician, Division of Rheumatology
and Clinical Immunology, Department of Medicine, UF COM - Jacksonville,
Jacksonville, FL. Karishma.Ramsubeik@jax.ufl.edu
Gurjit Kaeley, MD, Attending Physician, Division of Rheumatology and
Clinical Immunology, Department of Medicine, UF COM - Jacksonville,
Jacksonville, FL. Gurjit.Kaeley@jax.ufl.edu
Corresponding Author: Zachary Chandler, DO, Resident, Division of
General Medicine, Department of Medicine, UF COM - Jacksonville,
Jacksonville, FL. Zachary.Chandler@jax.ufl.edu
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.
Funding Statement: The author(s) received no financial support for
the research, authorship, and/or publication of this article.
Conflicts of Interest Statement: 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 non-financial
interest in the subject matter or materials discussed in this
manuscript.
Ethics Approval: An ethics approval was not required in our case due to
reported data being part of evaluation of patient and no patient
interventions performed.
Patient Consent Statement: Written consent was obtained from the patient
to publish his case.
Permission to Reproduce Material From Other Sources: No material from
outside sources used.
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.
CASE DESCRIPTION
A 58-year-old man presented for 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.
Vital signs were normal. Physical exam 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.
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.
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 4-5), third
(Figures 6-7), 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.
Patient was diagnosed with idiopathic knuckle pads and provided
reassurance about the benign nature of the findings.
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 Michaelangelo 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 decade 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, acrokeratoelastoidosis of Costa [2, 5-7]. 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 [8-10]. 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
[13-16]. Patients are often referred to rheumatologists for
evaluation and undergo evaluation for rheumatologic disease such as is
in the case of our patient. Distinguishing knuckle pads from synovitis
may be challenging on the basis of physical exam 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, 17-20].
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 [21-24]. Acquired knuckle pads such as in
the case of repetitive trauma should improve within months if the
offending insult is removed.
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.
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