INTRODUCTION
Eosinophilic fasciitis (EF) is a rare connective tissue disease
which presents with swelling and induration with
underlying fascial thickening.1 Medications such as
statins and phenytoin have been implicated in the causal pathway
of EF, suggesting that EF may be toxin-mediated in some
cases. Additionally, L-tryptophan is associated with development
of an eosinophilia-myalgia syndrome, demonstrating an
environmentally-induced eosinophilic autoimmune condition.2
However, the pathogenesis of EF remains unclear.
Dimethyl fumarate has recently been approved for use in
patients with multiple sclerosis (MS). Common side effects
include flushing and gastrointestinal events (eg, diarrhea,
nausea, upper abdominal pain).3 Fumaric acid esters, the
family of medications, which includes dimethyl fumarate,
have been previously used for psoriasis treatment and been
found to cause an increase in blood eosinophilia.4-7 Clinical
trials of dimethyl fumarate for MS treatment demonstrate
this same side effect.8 We present a case of an eosinophilic
fasciitis-like disorder temporally correlated with the initiation
of oral dimethyl fumarate.
CASE REPORT
A 36-year-old male with a history of relapsing-remitting multiple
sclerosis (MS) presented with left anterior thigh muscle
swelling and pain for 2 weeks. He had previously been treated
for MS with injectable interferon beta-1b for 16 years, which
he self-injected into his abdomen and thighs. During his 16
years of treatment with injectable interferon, the patient had no
skin changes at his injection sites or mobility limitations. Four
months prior to presentation, the patient switched from injectable
interferon treatment to oral dimethyl fumarate (Tecfidera).
Upon initiation of dimethyl fumarate treatment, he experienced
marked facial flushing. After his second week of dimethyl fumarate
treatment (240mg twice daily), he experienced strong
stomach cramping which subsided over two weeks. A few
weeks following initiation of treatment, the patient noticed
tightening and thickening of the skin on his right thigh. After
16 weeks of dimethyl fumarate treatment, he developed severe
left anterior thigh pain, one week following physical exercise
beyond his normal activity. This area became swollen, tender,
and erythematous. Magnetic resonance imaging (MRI) of the
left extremity showed skin thickening and subcutaneous ede-
