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Archive Articles
Dr Michael Rose
Conference Report written for Newsletter 55
December 2003 based on the talk at the Myositis Support Group Conference
2003 given by Dr Rose.
Inclusion Body Myositis
Dr Michael Rose is a neurologist at King’s
College Hospital, London. He has great expertise in diagnosing and
the management of Inclusion Body Myositis.
Dr Rose introduced the topics of how IBM is diagnosed, prospects
for treatment and how better treatments can be found.
Inclusion Body Myositis has a prevalence of 35.3 per million of
the population and is considered to represent 17-30% of the inflammatory
myopathies though this figure may be nearer to 70%. IBM is the commonest
acquired adult myopathy. Typically disease onset is after 50 years
of age and has a 3:1 male predominance.
IBM is diagnosed on clinical features and investigations. Clinical
features include symptoms (what the sufferer complains of) and signs
(what the doctor sees). Electromyography, creatine kinase levels
and muscle biopsy are investigations that are performed to confirm
diagnosis.
Most IBM is sporadic, meaning that it is not hereditary. There are
some instances where IBM may be hereditary. However most hereditary
forms actually refer to inclusion body myopathy and not inclusion
body myositis. The majority of IBM patients once seen in the clinic
for the first time can date back their muscle symptoms for at least
one or two years however as the muscle weakness is often gradual
it is difficult to define onset. Typically over this time the sufferer
starts to experience falls and buckling of the knee as a result
of weakness of the quadriceps. Additionally, the hand grip is weak,
a sign of distal weakness. Weakness is often asymmetrical and there
is trend that weakness affects the non-dominant side. Doctor examination
will look for evidence of proximal and distal muscle weakness typical
in IBM including, bilateral foot drop, inability to heel walk or
hop, an exaggerated lean and rocking out of chair, difficulty rising
from supine, ability to raise arms normally, and poor fist formation.
Dysphagia which can be minimal to severe is common in IBM (40-80%
IBM sufferers) and may precede limb symptoms. IBM sufferers do not
have pain, arthritis (except osteoarthritis of the knees), skin
rash, disease associated heart, lung or gastrointestinal problems.
The EMG and creatine kinase level provide clues as to the diagnosis.
The EMG will show myopathic changes and the creatine kinase level
may be raised. The definitive investigation for diagnosis is the
muscle biopsy (either needle muscle biopsy or open muscle biopsy).
Despite its distinct clinical features and characteristic muscle
biopsy it takes on average 8 years for a sufferer to be correctly
diagnosed with IBM. Delayed and misdiagnosis is common in IBM and
this may be because it is not well known to doctors. The clinical
features may be mistaken initially to resemble polymyositis. The
EMG can be misleading and may resemble motor neurone disease. The
muscle biopsy may not show all the features expected for IBM and
thus may again be mistaken to resemble polymyositis.
So how can IBM be distinguished from polymyositis? IBM is more common
in the male sex whereas polymyositis is more common in females.
Compared to polymyositis, IBM typically has a lower creatine kinase
level. IBM is slower in progression and the sufferer displays distal
as well as proximal weakness.
Treatment of IBM is controversial but treatment should be attempted
as it may slow down the progression of the disease. Treatment options
may include, steroids, azathioprine, cyclophosphamide, chlorambucil,
methotrexate, cyclosporine, total body irradiation, leukopheresis,
plasma exchange, intravenous immunoglobulin. Steroids, intravenous
immunoglobulin and beta interferon therapies have been investigated
in IBM but the results from these reports do not yet provide conclusive
information. The aims of treating IBM are improvement, stabilisation,
and slowing of progression. Finding new treatments for IBM will
require assessment and adoption of suitable drugs, and testing these
drugs in clinical trials. These clinical trials will require funding
but more importantly will require an appropriate number of patients
with the correct diagnosis taking part in the trials.
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