Myopathies with finger flexor weakness: Not only inclusion‐body myositis

Abstract

Muscle disorders are characterized by differential involvement of various muscle groups. Among these, weakness predominantly affecting finger flexors is an uncommon pattern, most frequently found in sporadic inclusion-body myositis. This finding is particularly significant when the full range of histopathological findings of inclusion-body myositis is not found on muscle biopsy. Prominent finger flexor weakness, however, is also observed in other myopathies. It occurs commonly in myotonic dystrophy types 1 and 2. In addition, individual reports and small case series have documented finger flexor weakness in sarcoid and amyloid myopathy, and in inherited myopathies caused by ACTA1, CRYAB, DMD, DYSF, FLNC, GAA, GNE, HNRNPDL, LAMA2, MYH7, and VCP mutations. Therefore, the finding of finger flexor weakness requires consideration of clinical, myopathological, genetic, electrodiagnostic, and sometimes muscle imaging findings to establish a diagnosis. K E Y W O R D S distal myopathy, finger flexor weakness, inclusion-body myositis, myopathy with rimmed vacuoles, myotonic dystrophy 2 | SPORADIC INCLUSION-BODY MYOSITIS sIBM is the most common acquired myopathy after 50 years of age. 3 Its pattern of upper limb muscle involvement has been extensively characterized by both clinical examination and imaging, 4-11 and primarily involves finger flexor muscles. The flexor digitorum profundus (FDP) and flexor pollicis longus are most frequently and most severely affected (Figure 1A,B), with weakness demonstrated in approximately 90% of sIBM patients. 5-7 Within the FDP itself, different fingers can be involved to different degrees. 12 The FDP inserts onto the distal

Distal Involvement and Subsarcolemmal Minicore-Like Areas in a Case of POGLUT1-Associated Myopathy

“…However, finger flexor weakness can also be found in some cases of genetic myopathies caused by ACTA1, CRYAB, DMD, DYSF, FLNC, GAA, GNE, HNRNPDL, LAMA2, MYH7, and VCP mutations. 3 We now add POGLUT1 mutations to this list. It is also noteworthy in needle EMG of the present case, the FLP showed myopathic changes, and the intrinsic hand muscles were preserved, and therefore the finger flexor weakness is not due to associated neuropathy.…”

Anti‐cN1A antibodies do not correlate with specific clinical, electromyographic, or pathological findings in sporadic inclusion body myositis

“…Perhaps the presence of anti‐cN1A antibodies in patients with rimmed vacuoles as the sole pathological finding on muscle biopsy and classic sIBM clinical features might favor the diagnosis of sIBM over a hereditary myopathy with rimmed vacuoles. However, owing to the reported variable specificity and sensitivity of these antibodies, heterogeneous phenotype and genotype of hereditary myopathies with rimmed vacuoles and overlap of clinical features among sIBM and hereditary myopathies, caution is advised and further studies in this regard are needed 9 …”

“…The muscle biopsy abnormalities have been crucial in defining the diagnostic criteria of sIBM, 6,7 but clinicians have emphasized the relevance of the clinical findings as diagnostic features 8 . At the same time, the finger flexor weakness, a classic feature of sIBM, is not very specific and can occur in other acquired and inherited muscle diseases, including inherited myopathies with rimmed vacuoles 9 . The search for a potential disease biomarker in sIBM led to the discovery of anti‐cytosolic 5′‐nucleotidase 1A (cN1A) antibodies 10,11 .…”

Inclusion body myositis: Update on the diagnostic and therapeutic landscape

“…It would be challenging to base the diagnosis solely on the quadriceps weakness, due to technical difficulty with manual muscle testing as mentioned above, and as the quadriceps may be involved to the same extent as hip flexors in some patients. While finger flexion weakness, more than shoulder abduction, can be more characteristic and easier to demonstrate, prominent finger flexion weakness can also be seen in other acquired (amyloidosis, sarcoidosis) and hereditary (especially myotonic dystrophy type 1) myopathies ( 23 ). Patients with atypical presentations pose additional diagnostic challenges with further delay in diagnosis ( 3 ).…”