Anti-Ku Myositis: A Potential Mimicker of Inclusion Body Myositis
Christina Istrate1, Laura Istrate2
1Neurology, Loma Linda University Health, 2Loma Linda University Medical Center
Objective:

To report a case of Anti-Ku Myositis presenting with symmetric proximal lower limb weakness, distal hand weakness, and esophageal dysmotility.

Background:
Anti-Ku myositis (AKM) is a low prevalence disorder presenting with weakness and concomitant systemic autoimmune disorders. While combined proximal and distal weakness has been described with this syndrome, distal weakness has been the predominant presentation of AKM. In the setting of the primary presentation being proximal lower extremity weakness, distal upper extremity weakness, and esophageal dysmotility, distinguishing AKM from IBM can be challenging.
Design/Methods:
N/A
Results:

A 77-year old female with history of arthritis, basal cell cancer, dysphagia with esophageal dilations, and Raynaud’s disease presented with history of progressive hip flexion weakness and trouble climbing stairs. Her exam was remarkable for bilateral psoas and quardriceps weakness and finger extension weakness. MRI L spine showed multilevel spondylosis with moderate spinal canal narrowing at L1-2 and L4-5. MRI right thigh/femur showed fatty atrophy of the distal quadriceps compatible with chronic myositis. Additional tests showed no abnormalities of: ACE-1, B12, aldolase, urine myoglobin, TSH/T4, myasthenia panel, ANA, Limb Girdle MD Panel, paraneoplastic panel, CK, or NT5c1A. NCS/EMG was unremarkable and negative for myopathic findings. Right quadriceps biopsy showed chronic myopathic changes, inflammation, but no rimmed vacuoles. She tested positive for Anti-Ku antibodies on the Myomarker 3 Plus panel and had a mildly elevated ESR. She previously tried IVIG without reported improvement. Upon confirming Anti-Ku antibodies, she was prescribed rituximab infusions. 


Conclusions:

  1. Anti-ku myositis is a rare inflammatory myopathy that can be clinically similar  to IBM making early differentiation crucial for appropriate treatment.

  2. While there are multiple treatments available for AKM, IBM has limited treatments.

  3.  Early immunosuppressive treatment for AKM can improve disease outcome resulting in less medical co-morbidities highlighting the importance for evaluation of other systemic symptoms and diagnoses via antibody testing.

10.1212/WNL.0000000000211676
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