Abstract
Background Gottron’s papules are a hallmark cutaneous finding of adult and juvenile dermatomyositis (DM), and their presence should suggest these diagnoses. In some cases, skin involvement can precede muscle disease or maybe the sole disease manifestation (amyopathic DM), making a correct diagnosis particularly important. Knuckle pads are a benign fibrotic condition that can look very similar to Gottron’s papules, appearing as erythematous or flesh-colored plaques over the dorsa of the interphalangeal (IP) joints. Primary knuckle pads are usually idiopathic but may be inherited as part of a genetic syndrome. Secondary forms (pseudo-knuckle pads) are caused by repetitive trauma.[1] This case illustrates the importance of distinguishing knuckle pads from Gottron’s papules to prevent unnecessary patient/parental concern and costly investigations.
Case Report A 7-year-old boy was assessed for suspected juvenile DM, with a 2-month history of raised erythematous lesions over the proximal and distal IP joints of both hands suggestive of Gottron’s papules. The rash was not painful or pruritic. He was otherwise asymptomatic with a negative review of systems, and no history of traumatic injury. Past medical and family history were non-contributory. A topical steroid had no effect on the rash. On examination, he appeared well, with pink papular and nodular lesions over proximal IP joints 1-5 and distal IP joints 2-5 bilaterally (Figure 1). Joint examination and muscle strength were normal; there were no nailfold abnormalities or other rashes. Laboratory investigations, including creatine phosphokinase, alanine transaminase, aspartate aminotransferase, lactate dehydrogenase and erythrocyte sedimentation rate were normal. Myositis-specific antibodies were negative; antinuclear antibody testing was positive for anti-RNP (low-titer). MRI of the pelvic girdle showed no evidence of myositis. The differential diagnosis of Gottron’s papules was reconsidered, and a diagnosis of knuckle pads was made based on their characteristic appearance. Skin findings more suggestive of knuckle pads rather than Gottron’s papules included their firm, smooth, and mobile nature and the well-demarcated, dome-shaped appearance of many of the lesions. No treatment was given and the lesions resolved spontaneously, as is commonly seen in children.
Conclusion Our case highlights the importance of recognizing knuckle pads as a mimic of Gottron’s papules. This will prevent misdiagnosis and allow rheumatologists to avoid unnecessary and expensive investigations. After inherited and secondary forms are excluded, patients can be reassured of the benign nature of this disorder.
References [1.] Vincek V. Dermatol Online J 2021;27:1-4.
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