FROM DERMATOMYOSITIS SINE DERMATITIS TO A COMPLETE FORM OF JUVENILE DERMATOMYOSITIS: AN INTRIGUING CASE REPORT!

Although rare, juveniledermatomyositis (JD) is the mostcommoninflammatorymyopathy in children. It is a vasculopathycategorizedintoclassical and non-classicalsubtypes, the latter includingamyopathicdermatomyositis (DM) and dermatomyositis (DM) withoutdermatitis. DM sine dermatitisis a rarelydescribedphenotype, representing an atypicalformwith no classiccutaneous manifestations, complicatingdiagnosis, and isthereforeidentified on the basis of well-defined diagnostic criteria.In this article, we report the case of a twelve-year-oldchildpresentingwith muscle weakness and myalgias one monthprior to admission. Clinicalexaminationrevealed a progressive myogenic syndrome withdysphagia to solids, with no other multi-visceralinvolvement or signs of severity. Mucocutaneousexaminationwaspoor, revealingonlyleukokeratosis of the leftlateralborder of the tongue, with no otherassociated skin signs. Muscle enzymes wereelevated. A myositis-specificautoantibodyassayrevealed a positive anti-NXP2. Electromyographyshowed a diffuse emyogenic syndrome. MRI of the lowerlimbsshowed diffuse hypersignal in the muscle tissue. A diagnosis of dermatomyositis sine dermatitiswas made, and treatmentwasinitiatedwith oral prednisone 2 mg/kg/day, combinedwithsubcutaneous Methotrexate 25 mg/week. In the absenceimprovementafter 5 months of treatment, weswitched to mycophenolatemofetil (MMF) at a dose of 600 mg/m² twicedaily, with good progression.Afterlosinghissight and stoppingtreatment for a long time, the patient returnedaftertwoyearswith a full clinicalpicture of juveniledermatomyositis, withsevere muscle weakness and skin signs. This time, given the severity of the disease, ourtherapeuticapproachwas to switch to third-line treatmentwithinfliximab 5 mg/kg biotherapyadministered at specificintervals, with good improvement.

幼年皮肌炎（juvenile dermatomyositis, JD）虽属罕见疾病，但却是儿童群体中最常见的炎症性肌病。该病属于血管病变范畴，可分为经典型与非经典型两个亚型，后者涵盖无肌病性皮肌炎（amyopathic dermatomyositis, DM）及无皮疹性皮肌炎。无皮疹性皮肌炎是一种罕见表型，属于无典型皮肤表现的非典型亚型，诊断难度较高，因此需依托明确的诊断标准方可确诊。

本文报告一例12岁患儿，入院前1个月即出现肌无力与肌痛症状。体格检查提示存在进行性肌源性综合征，伴固体食物吞咽困难，无其他多脏器受累表现或重症体征。黏膜皮肤检查结果有限，仅发现左侧舌侧缘存在黏膜白斑，未观察到其他伴随皮肤体征。肌酶水平升高，肌炎特异性自身抗体检测显示抗NXP2抗体呈阳性。肌电图检查提示弥漫性肌源性综合征。下肢磁共振成像（MRI）显示肌肉组织内存在弥漫性高信号。最终确诊为无皮疹性皮肌炎，予口服泼尼松2 mg/kg/天联合每周皮下注射甲氨蝶呤25 mg进行初始治疗。治疗5个月后症状无改善，遂调整治疗方案为吗替麦考酚酯（mycophenolate mofetil, MMF），剂量为600 mg/m²，每日两次，病情得到良好控制。

患儿后因视力丧失中断治疗并停药长达两年，再次就诊时已出现典型的幼年皮肌炎全套临床表现，伴严重肌无力与皮肤体征。鉴于此次病情严重程度较高，治疗方案调整为三线治疗：按5 mg/kg剂量给予英夫利昔单抗（infliximab）定期间隔生物制剂注射，患者症状得到显著改善。