Keywords
sarcoidosis - myositis - PET - FDG - fluoro-deoxyglucose
Introduction
While subclinical muscle involvement in sarcoidosis is frequent, symptomatic sarcoid
myopathy is a rare presentation of systemic sarcoidosis with multiple clinical forms
described in the literature. Fluoro-deoxyglucose positron emission tomography/computed
tomography (FDG-PET/CT) has been shown to be able to detect chronic myopathy, the
most common presentation that typically affects proximal muscle groups.
Case Report
A 65-year-old woman presented with increasing dyspnea for 2 months following tapering
of prednisone dosage to 10mg per day. She was otherwise being treated with oral methotrexate
25mg administered once a week and intravenous infliximab 5mg/kg administered every
8 weeks. She had been previously diagnosed with pulmonary and muscular sarcoidosis,
histologically confirmed by deltoid muscle and supraclavicular lymph node biopsies,
both demonstrating noncaseating granulomas. Electromyography of all four limbs was
classified as “irritable”, consistent with inflammatory myopathy. CT pulmonary angiography
was negative for pulmonary embolism. Gadolinium enhancement was absent on cardiac
magnetic resonance imaging (MRI). Echocardiogram was remarkable for an increased pulmonary
artery systolic pressure of 49 mmHg. Whole-body FDG-PET/CT was performed following
a myocardial suppression protocol (24 hour high-fat, low-carbohydrate diet, 12 hour
fasting, intravenous heparin) to exclude cardiac sarcoidosis ([Fig. 1A]). Incomplete myocardial suppression due to nonadherence to the preparation protocol
limited cardiac assessment. Uptake was absent at the thoracic and abdomen level. Intense
FDG uptake was noted in multiple upper body muscle groups, notably the scalene and
sternocleidomastoid (SUVmax=18.0) ([Fig. 1B]), trapezius, biceps, forearm, and paravertebral muscles ([Fig. 1C]). Patient denied any strenuous physical activity or trauma in the days preceding
the study. The patient's dyspnea was gradually relieved following prednisone dosage
increase, a switch from oral to subcutaneous methotrexate, and decreased dosing interval
of infliximab. Repeat FDG-PET/CT was performed a week later following strict adherence
to the preparation protocol, yielding a complete myocardial suppression ([Fig. 2A]). Pathological myocardial uptake was absent. Overall, muscle FDG uptake was significantly
reduced, with scalene and sternocleidomastoid SUVmax at 4.3 compared with 18.0 previously ([Fig. 2B]). Paravertebral muscle uptake intensity was reduced (SUVmax=4.4) ([Fig. 2C]). Trapezius and biceps abnormal uptake was resolved. New FDG uptake was noted in
the right masseter muscle (SUVmax=9.9) ([Fig. 2D]).
Fig. 1 (A) 18F-fluoro-deoxyglucose (FDG) positron emission tomography (PET) showing intense FDG
uptake in multiple upper body muscle groups (B and C) in a patient with histologically proven muscle sarcoidosis.
Fig. 2 (A)18F-fluoro-deoxyglucose (FDG) positron emission tomography (PET) performed following
treatment optimization showing important regression of FDG uptake in the upper body
muscle groups (B and C), while new FDG uptake was noted in the right masseter muscle (D).
Discussion
Sarcoidosis is a multisystem granulomatous disease of unknown origin. While asymptomatic
muscle involvement is common in systemic sarcoidosis (50–80%), symptomatic myositis
is a rare entity (< 0.5%).[1] Three patterns of sarcoid myositis have been reported: nodular, chronic, and acute
myositis.[1] Chronic myopathy is the most frequent type and typically presents in older women
as progressive proximal weakness and atrophy.[2]
[3] While sarcoidosis muscle involvement requires confirmation with a biopsy, many imaging
tests can aid in the diagnosis. Ultrasonography and CT scan can detect nodules but
are not useful for chronic myopathy and acute myositis. Atrophy of the muscles and
a high-signal intensity on T2-weighted imaging on MRI can suggest sarcoid muscle involvement.[1]
[2]
[3] However, FDG-PET/CT appears to be able to accurately detect chronic myopathy and
acute myositis in addition to being helpful for the initial diagnosis of sarcoidosis,
identifying extrapulmonary involvement, guiding biopsy, and monitoring treatment efficacy.[1]
[2]
[3] A variety of imaging findings on FDG-PET/CT have been described in patients with
myositis, ranging from focal symmetrical limb uptake to the presence of multiple linear
and patchy hypermetabolic lesions referred to as the “Tiger man sign.”[4]
[5]
[6] To the best of our knowledge, sarcoid myositis involving the neck muscles has not
been previously reported. In this case, the patient's presentation was most consistent
with chronic myopathy. Although active sarcoid myositis was not clinically suspected,
as in most cases because of nonspecific symptoms, FDG-PET/CT scan revealed active
muscle involvement. In patients with chronic myopathy, initial treatment with glucocorticoids
gradually tapered over 6 to 12 months is recommended. In patients with an inadequate
response following 3 months of glucocorticoids, treatment is escalated with the addition
of an immunosuppressive agent such as methotrexate or azathioprine. If myopathy remains
refractory, tumor necrosis factor (TNF) inhibitors such as infliximab and adalimumab
have been shown to be effective in case reports.[7]
[8] Indeed, TNF-α is recognized to play a role in initiating and maintaining granulomas.[7]
[8] Literature regarding the ability of FDG-PET/CT imaging to assess treatment response
in sarcoid myositis is very limited. Both Han et al and Dhomps et al reported cases
of complete response of sarcoid myositis on follow-up FDG-PET/CT scans, 18 and 4 months
following initiation of glucocorticoids, respectively.[5]
[9] Marie et al reported a case of sarcoid myositis refractory to prednisone and methotrexate
with favorable outcome 6 months following initiation of infliximab as evidenced by
normalization of abnormal muscle FDG uptake.[7] Our case is original as our patient had refractory muscular sarcoidosis despite
being treated with all three mainstays of treatment. FDG-PET/CT was shown to be useful
in assessing positive response as early as a week following dosage optimization. As
available data remains scarce, further investigations are necessary to determine the
role of FDG-PET imaging in muscular sarcoidosis follow-up.
