Case presentation
In September 2021, a 13-year-old boy presented to the emergency department of our medical facility complaining of fatigue and widespread edema over the last two months.  Additionally, he reported two bilateral painless subcutaneous masses on both sides of his neck with progressive growth over the past six months.
He was previously admitted to our center in August 2020 with generalized edema and a preliminary diagnosis of nephrotic syndrome. At that time, after performing an ultrasound-guided renal biopsy which showed segmental proliferation of the mesangial and endothelial cells, the diagnosis of FSGS was made. So, he was treated with pulse corticosteroid therapy (methylprednisolone 10 mg/kg/day) for three days, and after discharge, he underwent treatment with prednisolone with a dosage of 15 mg/day that was tapered by following weeks.
He also had a history of subclinical hypothyroidism. He denied a history of alcohol consumption or smoking; his family history was noncontributory to kidney or autoimmune diseases.
The patient’s vital signs at the time of admission were as follows: temperature 36.9°C, pulse rate 81 beats/minute, blood pressure 131/82 mm Hg, respiratory rate 17 breaths/minute, and oxygen saturation 98% on room air.
On examination, two non-tender, poorly mobile masses of 1.5 × 1 cm and 1.5 × 0.5 cm were located respectively in the right and left submandibular region of the neck with normal overlying skin. He had a 3+ pitting edema in both lower extremities. The remainder of the examination was unremarkable.
A chest radiograph showed no abnormal opacities, cavitations, or perihilar lymph nodes.
Laboratory findings of the patient are summarized in Table 1.
24-hour urine volume, proteinuria, and creatinine were reported 1100 ml, 3100 mg/day, and 1.4 mg/dL, respectively.
Urinalysis showed a specific weight of 1.025, red blood cells (15 cells/μl), and 2-4 granular casts in the urine sediment.
The results of rheumatologic and communicable disease screening tests were negative and in the normal range. Ultrasound examination of the thyroid gland showed thyroid lobes and isthmus with normal size and parenchymal echogenicity with no sign of solid or cystic lesion.
Ultrasonography of lymph nodes showed evidence of multiple lymphadenopathies on both sides of the neck, the largest of them measuring about 15 ×7 mm in the right submandibular region and 12 × 5 mm in the left carotid sheath.
In the setting of high serum levels of lactate dehydrogenase (LDH) and erythrocyte sedimentation rate (ESR), metastases of unknown origin and lymphoma were the highest diagnostic priorities, so the excisional biopsy of the largest mass (15 ×7 mm) was performed.
Microscopic examination of stained sections (Figure 1) showed lymph nodes with reactive follicles and prominent germinal centers. Eosinophilia and capillary hyperplasia were also evident. These histological characteristics were consistent with KD.
IgE serum levels were checked to make a definite diagnosis, which was reported 3425 g/L↑ (normal range, 0-200 g/L) with IgG, IgM, and IgA within normal ranges.
The treatment was started with oral prednisolone (15 mg/day) and mycophenolic acid (500 mg, bid), which resulted in a noticeable clinical improvement in the edemas and attenuation of proteinuria. The patient had a remarkable recovery and was discharged on day 10th of admission.
In a one-year follow-up, he was asymptomatic with lowered eosinophil count and no evidence of renal involvement relapse.