Sjögren’s syndrome (SS) is a systemic autoimmune disease characterized by disorders of the exocrine glands. Although SS has been considered rare in children, it is actually the fourth or fifth most common childhood collagen disease. Many pediatric patients do not complain of dryness; thus, a lot of cases are thought to go undiagnosed. Although the long-term prognosis of SS in children is unknown, early diagnosis and long-term follow-up are necessary because dry subjective symptoms and new extra-glandular organ damage may occur in some cases, and malignant lymphoma may develop in a small number of cases. The Diagnostic Guidance for SS in Childhood (2015) is helpful for early diagnosis. Early intervention to control the progression of symptoms and treatment is a future issue, so it is important to consider SS as a differential in daily medical care, to perform tests on suspected cases, and to avoid missing possible cases of SS.

Differences in the treatment of juvenile idiopathic arthritis (JIA) can be seen in different countries and can be confirmed from the guidance and guidelines developed in each country. JIA treatment in Japan is based on a combination of the “Guide to the Initial Treatment of Juvenile Idiopathic Arthritis 2015” and the “Guide to the Use of Biological Agents in Juvenile Idiopathic Arthritis, 2020 Edition”. Each is a collection of evidence plus the opinions of specialized departments for the guidance. In the United States, guidelines were developed in 2019 and 2021, and systematic review (SR) was conducted on set Clinical Questions (CQs) and recommendations were published. This tutorial paper describes the characteristics and differences of each guideline from an objective standpoint. In Japan, a new guideline for the treatment of JIA is currently being developed by the Ministry of Health, Labour and Welfare under the Research and Development of Intractable Disease Policy Project. Not only pediatric rheumatologists but also adult rheumatologists, ophthalmologists, and patient groups are participating in the development of these guidelines.

IgA vasculitis (IgAV) is a relatively common vasculitis syndrome in children, and recurrence of this condition is not uncommon. We report a case of acute appendicitis associated with IgAV recurrence which improved in response to conservative treatment. A 6-year-old boy complained of abdominal pain and purpura on both lower extremities. He was admitted to our hospital on the 7th day after the onset of symptoms due to exacerbation of the condition and was diagnosed with IgAV. Administration of prednisolone (PSL) 1 mg/kg/day rapidly improved symptoms and the patient was discharged on the 15th day after symptom onset. PSL was gradually discontinued and the patient did not report abdominal pain or purpura, but 11 days later, he visited the emergency department because of fever and upper and right lower abdominal pain (no purpura). He was admitted to the hospital; ultrasonography revealed acute appendicitis due to swelling of the appendix. Conservative treatment with cefmetazole (CMZ) improved the symptoms of appendicitis, but upper abdominal pain persisted and purpura appeared on both extremities. We considered these symptoms to be from IgAV recurrence. His symptoms improved rapidly with PSL, and the subsequent course was good. Although it is rare for IgAV to be complicated by acute appendicitis, appropriate treatment should be determined by performing imaging tests, such as ultrasonography or computed tomography, in addition to clinical findings.

There are various causes of hypercreatine kinasemia (hyperCKemia) including rheumatic diseases and hypothyroidism. Here, we reported the case of mixed connective tissue disease (MCTD) complicated with Hashimoto’s disease (HD), who developed hyperCKemia with each exacerbations of MCTD and HD. A 9-year-old girl with recurrent Raynaud’s phenomenon since the age of 7 years, developed fever, abdominal pain, neck pain, torticollis with cervical lymphadenopathy, hyperCKemia, and hypothyroidism. She was diagnosed with MCTD complicated with HD, and achieved remission with methylprednisolone pulse therapy. Thereafter, mycophenolate mofetil (MMF) was added, and remission was maintained. Levothyroxine (LT) was also started and was stopped after 4 months as thyroid function normalized. At the age of 10 years, the patient presented with abdominal pain, vomiting, and hyperCKemia, which was suspected to be an exacerbation of MCTD. However, at the same time, the exacerbation of hypothyroidism was also seen. LT was restarted and her symptoms were improved soon. At the age of 12, she developed neck pain, torticollis, and hyperCKemia again. Thyroid function was preserved with LT. The exacerbation of MCTD was suspected, and her symptoms and hyperCKemia improved after the doses of PSL increased. MCTD is frequently complicated with HD. Hypothyroid myopathy should be considered as a cause of hyperCKemia in patients with MCTD.

Thrombotic microangiopathy (TMA) is a serious complication of systemic lupus erythematosus (SLE) that reportedly occurs in parallel with increased SLE disease activity. We report the case of a girl who developed TMA soon after the onset and treatment of SLE, despite improvement in SLEDAI (SLE disease activity index) and serological markers. The 12-year-old girl had developed SLE with severe lupus nephritis. After the initial round of steroid pulse therapy, her platelet count increased and her anti-ds-DNA antibody titer decreased. However, her hemoglobin level and platelet count declined after the second round of steroid pulse therapy (day 12 of hospitalization), and even schistocytes were observed in a peripheral blood smear. Those suggested the development of TMA. On day 16, we commenced plasma exchange therapy and initiated treatment with intravenous cyclophosphamide and oral mycophenolate mofetil; on day 33, the schistocytosis resolved. Because TMA can develop at any time during the course of SLE treatment, clinicians should consider TMA as a possible complication in SLE patients who develop schistocytosis or experience any unusual changes in SLE disease activity.

An 8-year-old boy with a 3-week history of spiking fever and arthritis visited to the previous hospital. His blood tests revealed liver dysfunction and hyperferritinemia (ferritin 2,043 ng/mL), and he was referred to our hospital. On the first visit to our hospital, he presented a unique rash, so-called prurigo pigmentosa-like eruption, in addition to the typical evanescent rashes on his trunk. A diagnosis of s-JIA was made. After prednisolone administration was started, his symptoms, including the fever, arthralgias, and skin rash, improved. Various skin eruptions appear in adult-onset Still’s disease (AOSD), the adult form of s-JIA. However, those atypical eruptions rarely occur in s-JIA. The presence of the typical evanescent rash is important to establish the diagnosis. We should be aware that prurigo pigmentosa-like eruptions could appear in children with s-JIA and AOSD.

The cause of non-infectious uveitis is often unknown, and the one with tubulointerstitial nephritis is called tubulointerstitial nephritis and uveitis (TINU) syndrome. Although hyperthyroidism is rarely associated with TINU, we experienced a case of non-infectious uveitis associated with transient tubulopathy and hyperthyroidism at the same time. The patient was a 13-year-old girl who presented to her local ophthalmologist with a chief complaint of conjunctival hyperemia. She was diagnosed as uveitis and referred to our ophthalmology department. Although the uveitis improved with steroid eye-drops, her blood tests showed positive rheumatoid factor and urine tests showed high levels of NAG and β2 microglobulin (β2MG). In addition, high levels of free triiodothyronine (FT3) and free thyroxine (FT4), and low levels of thyroid-stimulating hormone (TSH) were found, and the patient was admitted to our hospital for a thorough examination. All autoantibodies associated with abnormal thyroid function were negative. Ultrasonography showed an irregular distribution of high and low echogenic areas in the thyroid gland. After 2 weeks of hospitalization, the levels of FT3, FT4 and TSH in the blood and the ones of urinary NAG and β2MG were normalized. In this case, tubulopathy and hyperthyroidism associated with non-infectious uveitis developed and went into remission at the same time. We believe that there is the mutual pathogenesis of these diseases, and we report this case based on the literature review.