Case report
This case report describes a familial cluster involving a 33-year-old Iranian woman and her two children, a 13-year-old daughter and an 8-year-old son, who presented with similar clinical manifestations.
The mother was admitted to our medical facility, presenting with a 3-week history of persistent fever and arthralgia affecting both ankles and knees. Additionally, she exhibited symmetrical, multiple, round, light pink, tender erythematous nodules with indistinct borders over the pretibial skin (Figure 1). The patient reported a preceding episode of respiratory symptoms, including cough, pharyngitis, fever, and lymphadenopathy, occurring 4 weeks prior to the onset of the skin lesions. Notably, there was no history of recent medication use, travel, COVID-19 vaccination, or exposure to individuals with infectious illnesses prior to the onset of symptoms.
One week after the mother’s respiratory symptoms began, her two children developed similar respiratory manifestations, including cough, pharyngitis, and fever. The daughter presented to our medical facility with a 3-day history of erythematous, tender nodules on her lower extremities. Physical examination revealed multiple, symmetric, erythematous, tender nodules measuring roughly 1.5 cm in diameter on the pretibial aspects of both lower legs. The lesions were similar in appearance to those observed in her mother’s case. No evidence of motor deficits or sensory abnormalities was noted, and distal pulses were palpable and symmetric. The patient reported mild discomfort during the examination of her ankles and knees. Systemic examinations were unremarkable, with no signs of mucous membrane involvement or lymphadenopathy.
The son presented with a 4-day history of similar erythematous, tender nodules on his lower extremities. Physical examination findings were comparable to those of his mother and sister, with multiple, symmetric, erythematous, tender nodules measuring approximately 1 cm in diameter on the pretibial aspects of both lower legs. No motor deficits, sensory abnormalities, or impairment of distal pulses were noted. The patient reported mild discomfort during the examination of his ankles and knees. Systemic examinations were unremarkable, with no evidence of mucous membrane involvement or lymphadenopathy.
Laboratory investigations were conducted for all three patients, including complete blood counts, renal and hepatic function tests, antistreptolysin O (ASO) titers, erythrocyte sedimentation rates (ESR), and C-reactive protein (CRP) levels. The mother’s white blood cell count was elevated at 11,000 cells/μL, consistent with leukocytosis. Her ASO titer was significantly increased at 333 IU/mL, suggestive of a recent streptococcal infection. The daughter’s white blood cell count was mildly elevated at 9,500 cells/μL, and her initial ASO titer was significantly elevated at 1067.6 IU/mL. A repeat test yielded a result of 327 IU/mL, still above the normal upper limit. The son’s initial ASO titer was within the normal range at 31.2 IU/mL; however, due to persistent symptoms, a repeat test was performed, revealing an elevated value of 100 IU/mL. All three patients had mildly elevated ESR and CRP levels, indicating the presence of underlying inflammation. Renal and hepatic function tests were within normal limits for all patients.
Imaging studies, including chest radiographs, were performed for all three patients and showed no abnormalities. Polymerase chain reaction (PCR) tests for COVID-19 were also conducted, and the results were negative.
The constellation of clinical findings, including the characteristic erythematous nodules on the lower extremities and the preceding respiratory symptoms, along with the laboratory abnormalities, particularly the elevated ASO titers and inflammatory markers, strongly support the diagnosis of EN secondary to a recent streptococcal infection in this familial cluster. The temporal relationship between the mother’s and her children’s respiratory symptoms and subsequent development of erythematous nodules suggests a shared environmental exposure to the streptococcal pathogen.