Juvenile dermatomyositis without skin lesions

Introduction An 8-year-old Iranian girl was referred because she had progressive muscle weakness predominantly in lower limbs since about 2 years ago. She was not able to stand from a sitting position without help and had difficulty climbing stairs. She walked slowly and could not run like before. She had no complaint of dysphagia or dysphonia. She was born through a normal vaginal delivery and had a history of neonatal jaundice treated with phototherapy. She was taking no medications and had no history of cutaneous disease or photosensitivity. Her parents mentioned no recent weight loss. Family history was negative for neuromuscular disorders. Her parents were not related. On physical examination, the patient was an alert young girl with stable vital signs; Oral temperature: 36.8, Heart rate: 88 beats/min, respiratory rate: 22/min, and blood pressure 115/70 mm Hg. Her weight was 23 kg. She had mild lumbar lordosis without pes cavus, no kyphoscoliosis or other musculoskeletal deformities. She had waddling gait with positive Gower’s sign. She was able to walk on heel and toe and had mild atrophy of hamstring muscles. There was no muscle tenderness. She had no facial weakness and no dysphonia. Her muscle forces were as: neck flexion 4/5, neck extension 4/5, proximal upper limbs 4/5, proximal lower limbs 3+/5, foot dorsiflexion, and plantar flexion were normal. Skin examination by an expert dermatologist showed no abnormalities on the face, hands or fingers. Ancillary investigations showed: Serum creatine kinase activity as 78. Serum aldolase level was also normal. Aspartate aminotransferase was 37 and Alanine aminotransferase was 19. Fluorescent antinuclear antibody (FANA), anti-neutrophil cytoplasmic antibody, anti–double-stranded DNA antibodies, and rheumatoid factor were all negative. Thyroid function tests, complete blood count, and urine analysis were also normal. Cardiological investigations were normal. Nerve conduction studies in upper and lower limbs were normal [including low-frequency and high-frequency repetitive nerve stimulation (RNS)]; but on needle examination all of the tested muscles in lower and upper limbs [deltoid], first dorsal interosseous (FDI), gluteus medius and maximus, rectus femoris, anterior, and gastrocnemius revealed typical myopathic pattern [small polyphasic motor unit action potentials (MUAPs) with early recruitment] without spontaneous activity [there was no fibrillation, positive sharp wave (PSW), myotonia or fasciculation]. She was referred for muscle biopsy and muscle biopsy from her left deltoid muscle reveal prominent typical perifascicular atrophy pattern in many fascicles (Figure 1a, 1C) with some foci of perimysial perivascular chronic inflammatory cell infiltration (Figure 1b). ATPase study revealed no fiber type grouping and atrophic fibers were both type 1 and 2. The diagnosis of dermatomyositis was made based on typical pathognomonic findings of her muscle biopsy. Iranian Journal of Neurology