Page 787 - Clinical Immunology_ Principles and Practice ( PDFDrive )

758 Part SIX Systemic Immune Diseases

bothersome symptom, but more often the patient is evaluated known as Gottron papules. In some cases, the metatarsophalangeal
for the physical limitations imposed by weakness: difficulty arising joints, elbows, knees, and malleoli show a similar rash. Both
from a low chair or bed, or combing and brushing hair. Rash is heliotrope and Gottron rashes can occur rarely in cases of frank
the first feature in a considerable proportion of patients who SLE without muscle involvement. Other common rashes include
have DM, but muscle weakness usually follows within a few a flat, red blanching eruption of the upper chest (often in a V
months. A subset of patients with DM, clinically amyopathic distribution), the upper back (where a shawl would touch), and
dermatomyositis (C-ADM), may present only with rash in the sometimes the extensor surfaces of the upper arms and thighs.
absence of muscle weakness throughout the course of their illness. Another rash that mimics the malar rash of lupus on the face
These patients are also at risk for pulmonary involvement, as may be present; however, in contrast to lupus, it does not spare
are those with classic DM. The prevalence of interstitial pneu- the nasolabial folds. Although found on sun-exposed parts of
monitis in C-ADM can approach 5–10%, compared with 40% the body, these rashes are often not photosensitive in nature. As
1
of patients with classic DM. Arthritis, Raynaud phenomenon, in other connective tissue diseases, nailfold capillary dilatation,
fever, or lung disease presenting as cough or dyspnea may infarcts, and cuticular overgrowth occur. Mechanic’s hands, a
dominate the clinical picture. Cardiac and gastrointestinal roughening and cracking of the radial sides of the fingers and
symptoms, other than dysphagia in severe cases, are rarely early the palm, resembling a condition found in people who labor
manifestations. Renal and central nervous system (CNS) involve- with their hands, is characteristic of a subset of myositis patients
ment are almost never a part of the IIMs. with the “antisynthetase syndrome” and can also be seen in
patients with PM-Scl and U1-RNP autoantibodies.
KEY CONCEPtS CLASSIFICATION
Definition and Incidence of Idiopathic
Inflammatory Myopathies (IIMs) In the past 40 years, several investigators have proposed diag-
nostic classification criteria for IIM. The criteria proposed by
• Polymyositis (PM), dermatomyositis (DM), and related inflammatory Bohan and Peter four decades ago remain the most familiar
muscle diseases are called IIM. and accepted definitions of PM and DM (Table 56.1). They
2,3
• Indistinguishable muscle inflammation may accompany other auto- combine clinical, laboratory, electrodiagnostic, and pathological
immune connective tissue diseases or limb-girdle muscular
dystrophies. features. These criteria currently serve as the gold standard for
• The annual incidence in the US is 5–10 cases per million. DM and clinical diagnosis and for inclusion in clinical trials. However,
PM are more common in women than in men in all age groups; they are limited by their poor specificity in distinguishing PM
inclusion body myositis (IBM) is more common in men. from other entities, including late-onset muscular dystrophies.
The resultant misclassification limits the homogeneity of the
patients included in previous observational and interventional
Some of the rashes of DM are virtually pathognomonic; others studies. Additionally, the Bohan and Peter criteria completely
are not disease-specific (Fig. 56.1). The heliotrope rash, a vio- omit the diagnosis of IBM, the most frequent type of IIM in
laceous discoloration of the eyelids, is sometimes no more than patients over 50 years of age.
a line along the margin of the upper lid, but it may also affect In 2004, more comprehensive criteria of IIM were proposed
both upper and lower lids completely and can be associated with and approved by a group of international experts (Table 56.2).
edema mimicking thyroid disease. A reddish, sometimes raised Unlike the previous criteria, these new criteria offer the advantage
and/or scaly, eruption over the metacarpophalangeal joints is of classifying two rare forms of autoimmune myositis, i.e., IMNM

A B
FIG 56.1 Dermatomyositis Rash. (A) In addition to the heliotrope rash on the eyelids of this
patient with dermatomyositis, there is a flat, red rash on the nose and cheeks. (B) A raised,
shiny-red rash—Gottron papules—is apparent on the interphalangeal and the second and third
metacarpophalangeal joints of this man with dermatomyositis.