APLAR Journal of Rheumatology 2007; 10: 83–85

©Asia Pacific League of Associations for Rheumatology

Blackwell Publishing AsiaEDITORIALEditorial

Dermatomyositis: the Asia-Pacific perspective

The idiopathic inflammatory myopathies (IIM) are agroup of autoimmune muscle diseases characterizedby chronic inflammation of muscles. This group can befurther categorized according to clinicopathologic fea-tures or presence of myositis-specific autoantibodies.The definition by Bohan and Peter1 for diagnosis ofdermatomyositis (DM) and polymyositis (PM) had beenused for over three decades. Though probably useful todistinguish IIM from other connective tissue diseases, ithad not been fully validated for its specificity to differ-entiate among different IIMs such as inclusion bodymyositis. Recently there was a proposal to enhance thediscriminatory power of the diagnostic criteria withincorporation of immunohistochemical findings.2 DMis distinguished clinically from PM by the presence ofpathognomonic photosensitive rashes over exposedareas. DM and PM share similar genetic risk factors butdiffer in their pathogenetic mechanisms. In DM, muscleand skin biopsies showed microangiopathic changeswith perivascular inflammation of B cells and CD4+ Tcells and complement-mediated vascular endothelialcell damage resulting in muscle ischaemia. On the otherhand, PM is characterized by clonally expanded CD8+cytotoxic T cells that invade and destroy via perforin-mediated mechanisms, myocytes which express MHCclass I antigens.3 Anti-aminoacyl-transfer RNA syn-thetase autoantibodies are found in both DM and PM,while antisignal recognition particle autoantibodies arelimited to PM, and anti-Mi-2 autoantibodies are diag-nostic for DM.

Accumulating evidence suggests that autoimmunediseases are often triggered by environmental factors ingenetically susceptible individuals. External factors suchas specific infections, vaccines, drugs, foods, agentsimplicated in occupational exposure and ultravioletradiation, have been suggested, although the exactmechanisms remain elusive. Ultraviolet radiation, inparticular, is known to increase the clinical expression

of conditions characterized by photosensitive rashessuch as lupus and DM. Indeed, the InternationalMyositis Collaborative Study Group had studied IIMcohorts in 15 cities and demonstrated that surfaceultraviolet radiation intensity most strongly contrib-uted to the relatively high proportion of DM and anti-Mi-2 autoantibodies in a dose-response manner.4 Forexample, the proportion of DM patients within an IIMcohort containing DM and PM was 79% in Mexico Cityas compared to 27% in Glasgow. This is of distinctrelevance to many Asian Pacific countries that arelocated in the tropical and subtropical regions whereabundant sunshine prevails.

Nonetheless, there are only handfuls of reports onthe clinical patterns of IIM (including DM) cohorts inAsian countries.5–8 On the other hand, there is evidencesuggesting that genetic predisposition to developmentof IIM as a whole differ in certain ethnic groups.Human leucocyte antigens and Gm/Km markers onimmunoglobulins have been associated with myositisand some myositis-specific autoantibody groups. In astudy comparing Koreans and American whites IIMpatients who had similar clinical and autoantibodyprofiles, HLA-DRB1*0301, the linked allele DQA1*0501,and DRB1 alleles sharing a specific motif in the firsthypervariable region were major genetic risk factorsfor the development of myositis in whites, but not inKoreans.9 On the other hand, Gm 21 was a protectivefactor for the development of IIM in Koreans but notin whites.

In many Asian countries infection presents a greatchallenge to the diagnostic process and subsequentmanagement of autoimmune inflammatory myositis.While parasitic muscle infestations and tropical pyomy-ositis are important differential diagnoses to exclude asthey deserve prompt specific antimicrobial treatment,myositis related to human immunodeficiency virus andprotozoan infection (e.g. Toxoplasma gondii) can be moresubtle and present as mimickers of IIM. Occasionallydisseminated cutaneous non-tuberculous mycobacte-rial infection can mimic panniculitis in patients withdefinite diagnosis of DM.10 Management of IIM often

Correspondence: Dr Moon-Ho Leung, Department of Medicine, Queen Elizabeth Hospital, Hong Kong. Email: leungmh@ha.org.hk

M.-H. Leung

84 APLAR Journal of Rheumatology 2007; 10: 83–85

involves use of high-dose corticosteroids which mightbe implicated in the development or reactivation oflatent tuberculosis, a situation which had been wellreported in systemic lupus erythematosus11,12 and rheu-matoid arthritis (even before use of biologics) in theAsian Pacific region.13 In particular, pulmonary tuber-culosis has to be seriously excluded in the work-up ofinterstitial lung disease which is known to be associ-ated with IIM. Again, this challenge is of paramountsignificance in many Asian countries where tuberculosisis still endemic.

Dermatomyositis is linked with interstitial lung diseaseand underlying malignancy, for which clinicians areearnestly searching during the entire course of illness.DM has been reported to be associated with a widespectrum of tumours and the overall risk as reported inCaucasian series is around 3–7 times, measured bystandardized incidence ratios by comparing with thebackground population risk.14,15 The risk is greatest atthe time of myositis diagnosis. The risk of malignancyassociated with PM appears to be slightly less than thatwith DM. Common malignancies associated with DMare lung, ovarian, cervical, gastric, colorectal and pan-creatic cancers and non-Hodgkin’s lymphoma. Nasopha-ryngeal carcinoma, common in the densely populatedareas of southern China but rare elsewhere, has beenreported to be associated with IIM and in particularDM in China,16 Hong Kong,17 Taiwan18 and Singapore.19

There are a number of relevant points here. Nasopha-ryngeal carcinoma was ranked the seventh top cancerin Hong Kong in 2004 and it is potentially curable withradiotherapy in the early stages. This tumour is signifi-cantly over-represented in a cohort of IIM patients inHong Kong, as the standardized incidence ratio wasestimated to be as high as 49 (95% CI: 18–107) (personalunpubl. data 2004). For these reasons, at the time ofdiagnosis of DM, surveillance of malignancy in patientsresiding in or coming from these regions should includestrategies particularly targeting at nasopharyngeal carcinoma,even in asymptomatic cases. Moreover, clinicians shouldbe aware of the potential, though uncommon, severecutaneous reaction after chemoradiotherapy for nasopha-ryngeal carcinoma, which might aggravate the existingskin lesions in DM.20

These specific considerations, together with manyothers, pose a great challenge to the diagnosis and man-agement of dermatomyositis in the Asia-Pacific region,which encompasses such an enormous and heterogene-ous population. Region-specific studies on clinicalfeatures, epidemiology, genetics, pathogenesis, treatmentoptions, treatment complications and association with

malignancy and interstitial lung diseases have long beenawaited. Only with a broader and deeper understandingon every aspect of DM can the outcomes of our patientsbegin to improve.

Moon-Ho LEUNG

Department of Medicine, Queen ElizabethHospital, Hong Kong

REFERENCES1 Bohan A, Peter JB (1975) Polymyositis and dermatomy-

ositis. (Parts I and II). N Engl J Med 292, 344–7.2 Dalakas MC, Hohlfeld R (2003) Polymyositis and dermat-

omyositis. Lancet 362, 971–82.3 Hohlfeld R, Engel AG, Goebels N, Behrens L (1997)

Cellular immune mechanisms in inflammatory myopathies.Curr Opin Rheumatol 9, 520–6.

4 Okada S, Weatherhead E, Targoff IN, Wesley R et al. (2003)Global surface ultraviolet radiation intensity may modulatethe clinical and immunologic expression of autoimmunemuscle disease. Arthritis Rheum 48, 2285–93.

5 Prasad ML, Sarkar C, Roy S, Bagchi U et al. (1992) Idiopathicinflammatory myopathy: clinicopathological observationsin the Indian population. Br J Rheumatol 31, 835–9.

6 Tong M (1995) A review of dermatomyositis cases atHospital Besar Kuala Lumpur 1989–93. Med J Malaysia50, 32–6.

7 Wong KO (1969) Dermatomyositis: a clinical investigationof twenty-three cases in Hong Kong. Br J Dermatol 81, 544–7.

8 Furuya T, Hakoda M, Tsuchiya N et al. (2004) Immunoge-netic features in 120 Japanese patients with idiopathicinflammatory myopathy. J Rheumatol 31, 1768–74.

9 Rider LG, Shamim E, Okada S et al. (1999) Genetic riskand protective factors for idiopathic inflammatory myo-pathy in Koreans and American whites: a tale of two loci.Arthritis Rheum 42, 1285–90.

10 Leung YY, Choi KW, Ho KM, Kun EW (2005) Dissemin-ated cutaneous infection with Mycobacterium chelonaemimicking panniculitis in a patient with dermatomyositis.Hong Kong Med J 11, 515–9.

11 Tam LS, Li EK, Wong SM, Szeto CC (2002) Risk factorsand clinical features for tuberculosis among patients withsystemic lupus erythematosus in Hong Kong. Scand JRheumatol 31, 296–300.

12 Mok MY, Lo Y, Chan TM, Wong WS, Lau CS (2005)Tuberculosis in systemic lupus erythematosus in an endemicarea and the role of isoniazid prophylaxis during corticos-teroid therapy. J Rheumatol 32, 609–15.

13 Yamada T, Nakajima A, Inoue E et al. (2006) Increasedrisk of tuberculosis in patients with rheumatoid arthritisin Japan. Ann Rheum Dis 65, 1661–3.

14 Hill CL, Zhang Y, Sigurgeirsson B et al. (2001) Frequencyof specific cancer types in dermatomyositis and polymy-ositis: a population-based study. Lancet 357, 96–100.

Editorial

APLAR Journal of Rheumatology 2007; 10: 83–85 85

15 Stockton D, Doherty VR, Brewster DH (2001) Risk of can-cer in patients with dermatomyositis or polymyositis, andfollow-up implications: a Scottish population-based cohortstudy. Br J Cancer 6, 41–5.

16 Hu WJ, Chen DL, Min HQ (1996) Study of 45 cases ofnasopharyngeal carcinoma with dermatomyositis. Am JClin Oncol 19, 35–8.

17 Teo P, Tai TH, Choy D (1989) Nasopharyngeal carcinomawith dermatomyositis. Int J Radiat Oncol Biol Phys 16, 471–4.

18 Peng JC, Sheen TS, Hsu MM (1995) Nasopharyngealcarcinoma with dermatomyositis. Analysis of 12 cases.Arch Otolaryngol Head Neck Surg 121, 1298–301.

19 Lee KH, Ong B, Lim TK, Chan HL (1994) Polymyositisassociated with symptomless nasopharyngeal carcinoma.Singapore Med J 35, 323–4.

20 Hareyama M, Nagakura H, Tamakawa M et al. (1995)Severe reaction after chemoradiotherapy of nasopharyngealcarcinoma with collagen disease. Int J Radiat Oncol Biol Phys1, 971.