DERMATOMYOSITIS AND POLYMYOSITIS
Dr. Vivek Rajagopal MD, MRCP
Consultant Rheumatologist
West Suffolk Hospital, Bury St Edmunds, UK
Introduction:
These are similar diseases caused by autoimmune inflammation of skeletal muscles. They
can be associated with extra muscular symptoms or occur along with another defined
connective tissue disease such as Sjogren’s syndrome, Lupus or Rheumatoid Arthritis.
Epidemiology
These are rare diseases. Epidemiological data are scarce and partly unreliable due to small
numbers.
The annual incidence is approximately 2 to 7 per million. Both polymyositis and
dermatomyositis have a female preponderance of 3:1. The peak age of onset is between 50
to 60; although cases have been described in all ages including children.
These disorders, particularly dermatomyositis are associated with malignancy. There is
approximately a 10 - 15% chance of finding a malignancy in patients presenting with
dermatomyositis. Usually, the malignancy precedes the muscle weakness, but the reverse
can also occur. The type of malignancies vary and include haematological malignancies
(mainly lymphoma), and solid tumours such as lung, ovary, breast and colon cancer.
Clinical Features
Muscle weakness and decreased muscle endurance are the predominant symptoms. Onset
is sub acute or insidious. Weakness is most pronounced in proximal muscle groups with a
symmetrical distribution. Some patients may experience muscle pain especially if myositis is
acute. If untreated, the weakness progresses slowly and in the most severe cases, patients
may become wheel chair bound. Swallowing difficulties, respiratory muscle weakness and
neck muscle weakness can also occur.
Cutaneous manifestations are seen in dermatomyositis. The skin rash may precede muscle
symptoms by months or years. The skin lesions may fail to respond to treatment. Several
types of lesions have been described:
i.
Gottron’s papules – the most specific skin lesion. These are violaceous, pink or dusky
red papules located over the dorsal side of metacarpal or interphalangeal joints.
ii.
iii.
iv.
v.
vi.
Heliotrope rash – A periorbital violaceous erythema of one or both eyelids with
oedema.
Red or violaceous erythema over the shoulders, neck and chest (the ‘V’ sign) or over
the hips.
Mechanic hands – Hyperkeratosis, scaling and fissuring of the fingers, particularly
over the radial side of index finger.
Other associated skin lesions are periungual erythema, nail fold telengiectasias and
cubicula overgrowth.
Calcinosis – Subcutaneous calcifications can occur. This is seen mainly in
dermatomyositis in children.
Involvement of other organs can also occur. Interstitial lung disease, cardiac involvement
with conduction disturbances and cardiomyopathy, arthralgia and arthritis, GI involvement
due to muscle weakness are some of the rare manifestations.
Differential Diagnosis
Infectious Myositis – Presents with acute muscle pain and weakness along with prodromal
features of the underlying infection. These are self limited. Infections associated with
myositis are influenza, echo and cox sackie viruses. Retroviral infections such as HIV and
HTLV – I (Human T cell Leukaemia/lymphoma virus) can cause myositis with clinical and
histological features similar to polymyositis. Focal myositis can be seen with staphylococcal
infections.
Drugs – Several drugs can induce myopathies with muscle weakness and increased
creatinine phosphokinase. The commonest drugs causing this are the statins. Other drugs
such as fibrates, nicotinic acid, cimetidine, chloroquine and colchicines are also associated
with myositis. Alcohol and glucocorticoid use can cause a chronic myopathy.
Inclusion body myositis – Presents with insidious onset muscle weakness, but does not
respond to immunosupressants. Characteristic distinguishing features are thigh extensor
and forearm flexor weakness. Dysphagia is common. Muscle biopsy is needed to make the
diagnosis.
Investigations
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Creatinine kinase – is elevated in most cases of inflammatory myopathies. 10 – 20%
of patients may have normal creatinine kinase levels. Other enzymes such as LDH,
ALT, and Aldolase can also be elevated.
Auto antibodies – are positive in 70%.The most frequently detected is a positive
ANA. There are myositis specific antibodies mainly directed against aminoacyl-t-RNA
synthetases. Anti Jo -1 is the most frequent and is available in tertiary centres.
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
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Electromyography (EMG) – Can detect the presence of myositis, but is not specific.
Its role is to identify the best site for muscle biopsy as multiple muscles can be tested
at the same time.
Muscle biopsy – is the definitive test and helps differentiate between Polymyositis
and Dermatomyositis. It can also be used to monitor response to treatment.
MRI – is increasingly used to identify inflammation within muscles and to monitor
treatment response.
Investigation to screen for malignancy
This is done at diagnosis and repeated if more specific symptoms arise. Usually a chest Xray, bone profile and baseline blood investigations are enough. CT of the chest, abdomen
and pelvis is increasingly being used as a screening examination.
Treatment
Steroids – Prednisolone 1mg/kg/day is very effective in resolving weakness and normalising
CK levels. Prolonged courses are usually required and response is gradual. Patients can
develop steroid induced myopathy which can be difficult to differentiate from relapse of
myositis. Steroid sparing agents; either methotrexate or azathioprine are often needed.
Most Rheumatologists prefer to start steroid sparing agents along with prednisolone at the
outset.
Other treatments
Plasma exchange has been used for severe cases with respiratory or bulbar weakness.
Intravenous immunoglobins have also shown to be effective as initial therapy in severe
myositis.
Cyclophosphamide and cyclosporine has been used in combination with glucocorticoids in
patients with lung involvement.
Infliximab, Etanercept and Rituximab have been used in refractory myositis with good
effect. Results of randomised controlled trials are awaited with interest.
Prognosis
More than 75% of patients make a full recovery. Often a period of physiotherapy and
rehabilitation is needed along with immunosuppressive treatment. A significant proportion
of patients experience treatment related morbidity mainly due to the adverse effects of
steroids. Periodic review is required to pick up malignancies early in dermatomyositis
patients.