reference from harrisons internal medicine

2. POLYMYOSITIS, DERMATOMYOSITIS, AND
INCLUSION BODY MYOSITIS:
INTRODUCTION;
The inflammatory myopathies represent the largest
group of acquired and potentially treatable causes of
skeletal muscle weakness.
They are classified into three major groups:
polymyositis (PM),
dermatomyositis (DM), and
inclusion body myositis (IBM).

3. POLYMYOSITIS
The actual onset of PM is often not easily determined,
and patients typically delay seeking medical advice for
several weeks or even months.
This is in contrast to DM, in which the rash facilitates
early recognition.
PM mimics many other myopathies and is a diagnosis
of exclusion.

4. DERMATOMYOSITIS and
INCLUSION BODY MYOSITIS
DERMATOMYOSITIS
DM is a distinctive entity identified by a characteristic rash accompanying, or
more often preceding, muscle weakness.
DM usually occurs alone but may overlap with scleroderma and mixed
connective tissue disease.
INCLUSION BODY MYOSITIS
In patients 50 years of age, IBM is the most common of the inflammatory
myopathies. It is often misdiagnosed as PM and is suspected only later when a
patient with presumed PM does not respond to therapy.

5. ASSOCIATION WITH
MALIGNANCIES
The incidence of malignant conditions appears to be
specifically increased only in patients with DM and not
in those with PM or IBM.
The most common tumors associated with DM are :
ovarian cancer, breast cancer, melanoma, colon
cancer, and non-Hodgkin lymphoma.

6. OVERLAP SYNDROMES
sclerotic thickening of the
dermis, contractures, esophageal
hypomotility, microangiopathy, and calcium deposits

7. ASSOCIATION WITH VIRAL INFECTIONS
Several viruses, including coxsackieviruses, influenza,
paramyxoviruses, mumps, cytomegalovirus, and
Epstein-Barr virus, have been indirectly associated with
myositis.

8. Differential Diagnosis
SUBACUTE OR CHRONIC PROGRESSIVE MUSCLE
WEAKNESS : This may be due to denervating conditions
such as the spinal muscular atrophies or amyotrophic
lateral sclerosis
ACUTE MUSCLE WEAKNESS : This may be caused by an
acute neuropathy such as Guillain-Barr
syndrome, transverse myelitis, a neurotoxin, or a
neurotropic viral infection such as poliomyelitis or West
Nile virus.

9. MYOFASCIITIS
NECROTIZING MYOSITIS
HYPERACUTE NECROTIZING FASCIITIS/MYOSITIS
(FLESH-EATING DISEASE)
DRUG-INDUCED MYOPATHIES

10. Treatment: Therapy of Inflammatory
Myopathies
1. Glucocorticoids. Oral prednisone is the initial treatment of choice;
2. Other immunosuppressive drugs. Eg Azathioprine, Methotrexate
3. Immunomodulation.
o Calcinosis, a manifestation of DM, is difficult to treat;
o IBM is generally resistant to immunosuppressive therapies.
Prednisone together with azathioprine or methotrexate is often
tried

11. THANK YOU