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electromyography and raised creatinine phosphokinase
levels. In eosinophilic polymyositis, diffuse and deep
infiltration of eosinophils into muscle occurs, with
pronounced perivenular eosinophilic cuffing [3,4]. In
contrast to focal eosinophilic myositis, muscle fibre
invasion is not common but necrosis may occur in areas
of dense infiltration [6]. Clinical presentation is distinct
from that of focal eosinophilic myositis. Tender muscle
swelling followed by proximal weakness accompanies a
systemic illness with myocarditis and heart failure. The
third subtype, eosinophilic perimyositis, has been
reported by several authors [4,7]. The eosinophilic
infiltrate is seen predominantly in the fascia and
superficial perimysium. Muscle fibres are usually
normal and fibre necrosis is rare. In contrast to focal
eosinophilic myositis and eosinophilic polymyositis,
peripheral blood eosinophilia is uncommon and creati-
nine phosphokinase levels are usually normal [7].
Our patient’s leukocytosis, striking eosinophilia and
the features of myositis all appear to fall within the
spectrum of focal eosinophilic myositis, which usually
affects the lower limbs. The involvement of the
sternomastoid [1] and deltoid [8] has also been reported.
Patients are otherwise well and symptoms usually
resolve spontaneously. Investigations reveal a raised
creatine phosphokinase (2–20 times normal) and focal
myositis features on electromyography. Histologically,
focal eosinophilic myositis is characterised by deep
perimysial infiltration. Eosinophils are evident even
within muscle fibres themselves, and this is associated
with necrosis. Skin and fascia are normal and there are
no perivascular infiltrates [4].
In most patients with eosinophilic myositis the
aetiology is unknown. The pathogenesis of eosinophilic
myopathy remains undefined. It is possible that,
following an unknown triggering event such as trauma,
ethanol ingestion, or exposure to some other agent, there
is an increase in eosinophil production and activation
mediated by cytokines known to be important for the
growth and maturation of eosinophils [3]. Pathologic
studies of focal eosinophilic myositis have revealed fibre
size variation, angular fibres, hypertrophy, fibre splitting
and interstitial fibrosis, which are less common
findings in polymyositis and are different from the
histopathologic changes of eosinophilic myosites.
Myofibre necrosis and regeneration, associated with
perimysial and endomysial mononuclear infiltration
without eosinophils, defines the inflammatory lesion of
focal eosinophilic myositis.
Fig. 1. Transverse section of a muscle biopsy specimen from a patient
with idiopathic eosinophilic myositis stained with Gomori trichrome.
Muscle fibres are surrended by not only mononuclear cells, but also
eosinophils containing red-positive granules.
RNP antibody and anti-Jo-1 antibodies were negative.
Further immunologic studies revealed an elevated level
of serum IgE (3.62 uA/ml; normal 50.34 uA/ml), with
specific IgE reactivity on RAST testing to house dust
mite (Dermatophagoides pternoyssinus and Dermato-
phagoides farinae). IgA, IgM, IgG, C3 and C4 were
within normal ranges. The electrocardiogram was
normal. The electromyogram showed myogenic change
in the biceps and triceps of the arm, the biceps and
quadriceps of the thigh, and the triceps of the calf.
Muscle biopsy specimens from the left of the left
swelling biceps brachii demonstrated infiltration with
many monocytes and eosinophils at the perimysium and
endomysium. The number of eosinophils was 57 ꢀ 11/
2
mm (Fig. 1). A small number of necrotic fibres were
detected.
A diagnosis of focal eosinophilic myositis was made
and the patient responded promptly to oral prednisone
4
0 mg daily. His responses returned to normal after 1
week of therapy, as did serum CK, aldolase, WBC and
eosinophils.
Discussion
Eosinophilic myositis consists of a clinically and
pathologically diverse group of disorders. Inflammatory
muscle diseases associated with peripheral and/or tissue
eosinophilia are rare [3].
Idiopathic eosinophilic myopathy may be classified
into three subtypes: focal eosinophilic myositis, eosino-
philic polymyositis, and eosinophilic perimyositis [4]. In
focal eosinophilic myositis deep eosinophilic infiltration
of muscle and muscle fibres is seen, usually with
associated necrosis of adjacent myocytes [1,5]. Typically
there is evidence of peripheral blood eosinophilia, in
addition to the features of myositis, such as abnormal
Treatment for eosinophilic myositis has been reported
to result in either a spontaneous recovery or a steroid-
induced relapse [5]. In each case a subsequent relapse
was also promptly controlled by prednisolone therapy.
Non-steroidal anti-inflammatory agents also appeared
beneficial in mild episodes. In our case, treatment with
daily prednisolone 40 mg resulted in the resolution of
symptoms and normal CK levels.
Eosinophilic myopathic syndromes represent a hetero-
geneous group of rare conditions. We report a case of
eosinophilic myositis, the cause of which might be