To the editor: The diagnosis of juvenile dermatomyositis (JDM) is much more challenging when lacking the cutaneous manifestations as well as muscular biomarkers. Here we report an interesting case of JDM.
A 15-year-old boy was admitted to our hospital due to progressive weakness of limbs for about one year. He reported a weight loss of 5 kg and no family history of musculoskeletal disease. On physical examination, his cheek was a little swelling, but there was no rash or lymphadenopathy. Neurologic examination revealed muscle atrophy in the trunk and limbs while muscle tenderness was negative. Bilateral symmetric muscle weakness affected the proximal shoulder and hip-girdle muscles in the scale of 2-3. He was walking in a waddling gait while the Gower's sign was positive. The deeptendon reflexes diminished in four extremities. The remainder of the examination revealed no abnormalities. The test of creatine kinase (CK) was normal while lactate dehydrogenase (LDH) was elevated. Electromyography (EMG) and nerve conduction studies were consistent with muscular injury.
During his hospital stay, reddish-purple rash gradually appeared on the swelling upper eyelids of this patient, which was confirmed as the “Heliotrope rash” by the dermatology consultation. Telangiectasia of the eyelid capillaries could also be seen (Figure 1A and 1B). At last, muscle biopsy from the patient's proximal quadriceps showed degeneration of muscle fibers and perifascicular atrophy along with perivascular mononuclear infiltrate, which are the characteristic histological findings of dermatomyositis (Figure 1C and 1D).
As we know, CK is the most sensitive indicator of muscle injury, and is the best measure of the course of muscle injury.1 In a retrospective study of 166 patients with JDM, Pachman et al2 reported normal serum levels of CK, LDH, and aldolase in 26, 13, and 17 percents of patients, respectively. In one study of 16 patients with JDM, elevations of serum LDH and AST were associated with disease flare.3 The risk of disease flare within the next 4 months increased three-fold following a 20% rise in serum AST levels. However, an association with disease flares was not seen with either an elevation of serum ALT or CK. It seems that the CK levels were more likely to be normal with prolonged disease duration prior to treatment, particularly beyond 4 months. This case emphasized that we should also take a dialectical view towards CK since it is acting like a double-edged sword in the diagnosis of inflammatory myopathy. Elevated serum CK is supportive for myositis, but normal CK levels do not exclude them, since the level of CK are correlated with other factors especially the duration.
1. Bohlmeyer TJ, Wu AH, Perryman MB. Evaluation of laboratory tests as a guide to diagnosis and therapy of myositis. Rheum Dis Clin North Am 1994; 20: 845-856.
2. Pachman LM, Abbott K, Sinacore JM, Amoruso L, Dyer A, Lipton R, et al. Duration of illness is an important variable for untreated children with juvenile dermatomyositis. J Pediatr 2006; 148: 247-253.
3. Guzman J, Petty RE, Malleson PN. Monitoring disease activity in juvenile dermatomyositis: the role of von Willebrand factor and muscle enzymes. J Rheumatol 1994; 21: 739-743.