Muscle ultrasonography: a potential new tool to diagnose and evaluate treatment in dermatomyositis and polymyositis

Optimal and quick diagnosis of idiopathic inflammatory myopathies such as
dermatomyositis (DM) and polymyositis (PM) is important as these are treatable
conditions. At this moment treatment effect is mainly based on clinical
evaluation and functional scores, whereas other investigations
(electromyography (EMG) and muscle biopsy) are difficult to repeat, because of
its invasiveness. New diagnostic and objective instruments to aid in the
diagnosis and monitoring treatment are therefore necessary. Ultra sound imaging
(US) is easily applicable and proves to be useful in detecting various
neuromuscular disorders. Muscle US might be of additional value in diagnosing
DM and PM and might also aid in evaluating treatment response.

The aim of this study is to assess the diagnostic and monitoring properties of
muscle US and to investigate if US is able to distinguish a myositis flare-up
from a steroid-induced myopathy.

Patients suspected for the diagnosis will be invited to take part in this
prospective follow-up study. Additional to standard care muscle US and MRI will
be performed. Furthermore, muscle force will be assessed by dynamometry and
muscle function test (FI-2).
Newly diagnosed patients and patients that have been diagnosed will be
requested to participate in the assessment of monitoring properties of US.
Patients will be followed for one year in which muscle US, Health Assessment
Questionnaire (HAQ), dynamometry and FI-2 will be assessed at a 3 month
interval. In addition MRI, EMG and muscle biopsy will be performed at the end
of this follow-up year.
Patients that have been diagnosed and newly diagnosed patients will also be
invited to participate in a prospective follow-up during the full length of
the study to monitor a possible myositis flare-up. In case of possible myositis
flare-up US will be repeated. Patients with a steroid-induced myopathy will be
selected from the department of Hematology and Gastroenterology to serve as
controls.

Muscle ultrasound assessment and questionnaires are not a large burden for the
participants of this study. EMG and muscle biopsy are the 2 most invasive
procedures, certainly at the moment of active disease (at diagnosis or during
flare-up of the myositis). In this study this investigations will performed 12
months after diagnosis or flare-up to making it less painfull for patients as
possible. In addition participants could indicate to let the EMG and muscle
biopsy not be performed. However, for the study it would be better to perfom
EMG and muscle biopsies in all participants, but in our opinion this would have
been a to great burden for the patients.