CASE Reumatismo, 2021; 73 (1): 67-69 REPORT Knuckle pads mimic early psoriatic arthritis I. Giovannini1, S. Zandonella Callegher1, E. Errichetti2, S. De Vita1, A. Zabotti1 1Department of Medical and Biological Science, Rheumatology Clinic, University of Udine, Italy; 2Institute of Dermatology, “Santa Maria della Misericordia” University Hospital, Udine, Italy SUMMARY Knuckle pads or Garrod’s nodes are a rare, non-inflammatory condition. They consist of benign, well-circum- scribed fibro-adipose tissue over the small joints of hands and feet. Knuckle pads may be under-diagnosed and mistaken for early arthritis. The rheumatologist should perform an accurate differential diagnosis in which he can be helped by ultrasound and by other colleagues, such as the dermatologist. Ultrasound is considered useful in the assessment of the thickening of the subcutaneous tissue, located usually on the extensor site of proximal interphalangeal and metacarpophalangeal hand joints. Dermoscopy may play a role in detecting epidermal and dermal changes. We hereby report the case of a female patient with knuckle pads mimicking psoriatic arthritis. Key words: Knuckle pads, Garrod’s nodes, psoriatic arthritis, ultrasound, dermoscopy. only Reumatismo, 2021; 73 (1): 67-69 use n INTRODUCTION n CASE REPORT he evaluation of small joint swelling We report the case of a 30-year-old previ- Tin young patients is often challenging. ously healthy woman with reddish, occa- This clinical manifestation should be dif- sionally painful swelling of the right hand ferentiated from a joint disease as well as proximal interphalangeal (PIP) joints, who from lesions of the para-articular tissues, presented to our rheumatology clinic to such as soft tissue growth or other masses. have a second opinion for a suspected pso- In young patients, the swelling of the small riatic arthritis (Figure 1a). joints of the hands is usually related to The swelling appeared a year earlier, ini- inflammatory diseases (e.g., psoriatic ar- tially in the 2nd and 4th right PIP joints, then thritis, rheumatoid arthritis, connective tis- extended to the 3rd and 5th right hand PIP sue diseases), but also non-inflammatory joints, associated with redness and local conditions should be consideredNon-commercial in the pain (Figure 1a). The patient’s sister suf- differential diagnosis. Non-inflammatory fered from psoriasis and their mother had diseases presenting with swelling of the frequently uveitis. Blood investigations re- small joints of the hands could be caused vealed negative anti-nuclear antibodies, ex- by a local lesion, such as synovial cyst and tractable nuclear antigen panel, rheumatoid giant cell tumor or a systemic disease (e.g., factor, anti-citrullinated peptide antibodies acromegaly). and C-reactive protein. The patient com- Imaging, such as magnetic resonance or plained about local mild pain symptoms ultrasonography (US), is useful in differen- and had no signs of inflammation in PIP tial diagnosis, particularly in doubtful cas- joints. No other joint was affected. Because es. US, which is nowadays part of routine of the swelling with redness and the family clinical practice especially in early arthritis history of psoriasis, psoriatic arthritis was management, could assist the clinician to suspected, and sulfasalazine 2 gr/die was Corresponding author: identify the involved structures and the de- proposed. However, the patient reported no Salvatore De Vita gree of inflammation and damage, even in improvement. Rheumatology Clinic, Santa Maria della Misericordia, the pre-clinical phases of psoriatic arthritis US and dermoscopy were used for the dif- University Hospital, Italy (1). ferential diagnosis of joint swelling. US E-mail: [email protected] Reumatismo 1/2021 67 CASE REPORT E. Marasco, M. Mussa, F. Motta, et al. (Samsung RS 85) highlighted a hypoechoic n DISCUSSION area over the central slip of the third right extensor tendon, without joint involvement Knuckle pads are benign subcutaneous and without any signs of synovitis or en- nodules that appear most frequently on thesitis (Figure 1b). Dermoscopy revealed the small joints of the hands. In children, lesions with white scaling and white-yel- they are often idiopathic, and no univer- low areas, histologically corresponding sally effective treatment has been reported. to hyperkeratosis and underlying fibrosis, Knuckle pads or Garrod’s nodes are be- respectively (Figure 1c). Subsequently, the nign fibro-adipose pads located in the sub- diagnosis of psoriatic arthritis was not con- cutaneous tissues over the small joints of firmed, based on clinical signs and imaging hands and feet and could be mistaken for features, whereas knuckle pads were diag- arthritis or dermal lesions (2, 3). nosed. The patient was successfully treated These lesions usually present as slowly with a combination of topical canthari- enlarging, painless pads, typically located din -odophyllotoxin - salicylic acid. on the extensor site of the small joints of the hands [in particular PIP and metacar- pophalangeal (MCP) joints]. Knuckle pads have been associated with repetitive fric- tion or pressureonly (e.g., habitual chewing or sucking of the fingers, repetitive occu- pational activities, athletic activities like useboxing and surfing and bulimia nervosa with self-induced vomiting), fibrosing dis- orders (Dupuytren’s contracture, Ledder- hose’s syndrome/plantar fascial fibromato- sis and Peyronie’s disease) and autosomal dominant syndrome (Bart-Pumphrey syn- drome), but idiopathic cases have also been described (4). In our patient ultrasonography showed a hypoechoic subcutaneous thickening on the dorsal side of affected MCP or PIP joints. These pads had a dome shape with irregular borders. Generally, they consist of non-compressible nodules without pow- er Doppler signal, unlike what happens in Non-commercial psoriatic arthritis (4). Some hypervascular- ization may be rarely detected in the pe- ripheral area (5) (Figure 1). The adjacent joints and tendons are usually normal. As recommended for PsA, a clinical and ultrasound examination of the affected region with a high-resolution ultrasonog- raphy is needed to perform an accurate assessment of the joints and adjacent soft tissues (6). Also a joint rheumatological and dermatological assessment can be use- Figure 1 - a) Knuckle pad lesions over the finger joints (proximal interphalan- Figure 1 - a) Knuckle pad lesions over the finger joints (proximal interphalangeal joints of the rightful (7). Dermoscopy may also be helpful hand);geal joints b) Ultrasonographic of the right hand); assessment b) Ultrasonographic of knuckle pads: hypoechoic assessment area ofover knuckle the central pads: slip of the thirdhypoechoic right extensor area overtendon. the Joint central and sliptendon of theinvolvement third right were extensor not detected; tendon. c) DermoscopicJoint (8, 9), as it may show epidermal alterations evaluation of knuckle pads revealing epidermal and dermal changes (left). Knuckle pads(scaling due to hyperkeratosis) and der- dermatologicand tendon clinical involvement evaluation were (right). not detected; c) Dermoscopic evaluation of knuckle pads revealing epidermal and dermal changes (left). Knuckle pads mal alterations (white-yellow areas corre- dermatologic clinical evaluation (right). sponding to fibrosis), which reflect the his- 68 Reumatismo 1/2021 7 CASE Denosumab for the treatment of HIV-associated osteoporosis REPORT tological alterations seen in knuckle pads dermodactyly: the role of ultrasonography and (10). There is no effective treatment for dermoscopy for diagnosis. Rheumatology. knuckle pads (11). Behavior changes and 2017; 56: 703-703. 4. Hyman CH, Cohen PR. Report of a family psychiatric support may show results, oth- with idiopathic knuckle pads and review of id- erwise watchful waiting is recommended. iopathic and disease-associated knuckle pads. Some case report described some efficacy Dermatol Online J 2013; 19: 18177. of local treatments, such as intralesional 5. Lopez-Ben R, Dehghanpisheh K, Chatham fluorouracil or antharidin-podophylotoxin- WW, et al. Ultrasound appearance of knuckle salicylic acid (12, 13). pads. Skeletal Radiol. 2006; 35: 823-7. 6. Zabotti A, Piga M, Canzoni M, et al. Ultra- sonography in psoriatic arthritis: which sites n CONCLUSIONS should we scan? Annals of the Rheumatic Dis- eases. 2018; 77: 1537-8. In conclusion, in cases of joint swelling of 7. Savage L, Tinazzi I, Zabotti A, et al. Defining the hand joints mimicking arthritis, care- pre-clinical psoriatic arthritis in an integrated dermato-rheumatology environment. J Clin ful history taking may suggest non-inflam- Med Multidis Digital Publ Inst. 2020; 9: 3262. matory diseases. The diagnosis of knuckle 8. Zabotti A, Errichetti E, Zuliani F, et al. Early pads can be readily made by clinical exam- psoriatic arthritis versus early seronegative ination and ultrasonography. Dermoscopy rheumatoid arthritis: role of dermoscopyonly com- might also be useful to assist clinicians in bined with ultrasonography for differential di- doubtful cases. agnosis. J Rheumatol. 2018; 45: 648-54. 9. Errichetti E, Zabotti A, Stinco G, et al. Der- moscopy of nail fold and elbow in the differ- Conflict of interests ential diagnosis of earlyuse psoriatic arthritis sine The authors declare no potential conflict of psoriasis and early rheumatoid arthritis. J Der- interests. matol. 2016; 43: 1217-20. 10. Kodama BF, Gentry RH, Fitzpatrick JE. Pap- ules and plaques over the joint spaces. Knuck- n REFERENCES