Abstract Details

Title Atypical Presentations of Inclusion Body Myositis

Topic Neuromuscular and Clinical Neurophysiology (EMG)

Presentation(s) P15 - Poster Session 15 (5:30 PM-6:30 PM)

Poster/Presentation
Number 11-002

Background Typically, IBM presents with progressive weakness preferentially involving finger flexors and quadriceps muscles. Little is known about its atypical presentations.

Objective To identify the frequency and describe the clinical characteristics and outcomes of Inclusion body myositis (IBM) patients with atypical presentation.

Design/Methods We retrospectively searched the Mayo Clinic medical records to identify IBM patients with atypical disease onset, seen between 2015 and 2020. IBM diagnosis was made either by fulfilling the 2011 European Neuromuscular Center (ENMC) criteria at a later point during the disease course, or by having all 3 histopathological features of endomysial inflammation focally invading non-necrotic muscle fibers, rimmed vacuoles, and congophilic inclusions.

Results We identified 357 patients with IBM, of whom 50 (14%) had an atypical disease onset. The most common presentation was dysphagia 25 (50%) followed by asymptomatic hyperCKemia (24%), then foot drop (12%). Three patients presented with proximal arm weakness (6%), 2 (4%) with axial weakness and 2 (4%) with facial diplegia. Mean onset to diagnosis was 9 years. Median age at diagnosis was 70.5 years (range 40-86). Patients presenting with dysphagia were more commonly females. When tested, 32/37 (86.5%) patients had impaired swallowing. CK elevation was seen in 84% of patients. Only 1 out 26 patients who received immunotherapy had mild clinical improvement, mainly in dysphagia. Most patients had generalization of their weakness with time, reflected by a decline in their strength summated score with a slope of -0.082 (per month). Thirty-seven (74%) patients eventually satisfied ENMC criteria for IBM.

Conclusions

A significant proportion of IBM patients may have an atypical presentation. Recognition of such heterogeneity of the disease improves early diagnosis, prevents unnecessary immunotherapy, and provides insight for future diagnostic criteria and clinical trials.

Authors/Disclosures
Mazen S. Alamr, MBBS (Mayo Clinic) PRESENTER	Dr. Alamr has nothing to disclose.
Marcus Vinicius R. Pinto, MD (Mayo Clinic)	Dr. Pinto has nothing to disclose.
Elie Naddaf, MD (Mayo Clinic)	Dr. Naddaf has received personal compensation in the range of $5,000-$9,999 for serving as a Consultant for Expert Connect. The institution of Dr. Naddaf has received research support from NIAMS. The institution of Dr. Naddaf has received research support from American Neuromuscular Foundation. The institution of Dr. Naddaf has received research support from Fulcrum therapeutics. The institution of Dr. Naddaf has received research support from Abcuro. The institution of Dr. Naddaf has received research support from Cabaletta .