Which conditions are included in the differential diagnoses of sporadic inclusion body myositis (s-IBM)?

Updated: Jun 08, 2018
  • Author: Michael P Collins, MD; Chief Editor: Nicholas Lorenzo, MD, MHA, CPE  more...
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Answer

Acid maltase deficiency

Hereditary inclusion body myopathy

Motor neuron disease

Post polio syndrome

Oculopharyngeal muscular dystrophy

Late-onset distal myopathies

Overlap myositis

Sarcoidosis (chronic atrophic sarcoid myopathy)

Drug-induced myopathies

Myotonic dystrophy, type 1/2

Myofibrillar myopathies

Table 1. Clinical Differential Diagnosis of s-IBM (Open Table in a new window)

Disease

Points of Differentiation

h-IBM

Clinically and genetically heterogeneous group of diseases; positive family history; muscle biopsy features similar to s-IBM, but no inflammation

Polymyositis (PM)*

Weakness usually symmetric and proximally predominant; occasional cardiac and pulmonary involvement; similar to s-IBM, biopsy shows endomysial inflammation with invasion of non-necrotic fibers by CD8+ cells, but unlike s-IBM, rimmed vacuoles and ragged red fibers are infrequent and amyloid deposits and tubulofilaments not seen (see Histologic Findings)

Dermatomyositis (DM)

Weakness usually symmetric and proximally predominant; occasional cardiac and pulmonary involvement; characteristic skin lesions; characteristic biopsy findings (eg, perifascular atrophy, muscle infarcts, microvascular MAC deposits in the endomysium, focal capillary depletion, and conspicuous alterations in endothelial cells of endomysial microvasculature)

Oculopharyngeal muscular dystrophy (OPMD)

Predominant involvement of oculopharyngeal musculature (no extraocular muscle involvement in s-IBM); biopsy shows vacuoles, myopathic changes, and infrequent tubulofilaments (similar to s-IBM) but no inflammation; biopsy also shows pathognomonic intranuclear filamentous inclusions having smaller diameters than s-IBM tubulofilaments in 2-9% of nuclei; genetic testing is available for OPMD (PABPN1 gene); rare, genetically distinct oculopharyngodistal variant in Japan

Late-onset distal myopathies

Clinically and genetically heterogeneous group of diseases; positive family history unless sporadic case; biopsy may show rimmed vacuoles and tubulofilamentous inclusions in Welander, distal myopathy, Nonaka distal myopathy, and tibial muscular dystrophy, all of which can be classified as h-IBM. Gene testing is available for Nonaka distal myopathy (GNE) and tibial muscular dystrophy (titin).

Overlap myositis

PM- or DM-like clinical and myopathological presentation but with additional systemic and serologic features diagnostic of an underlying connective tissue disease (eg, systemic lupus erythematosus, Sjögren syndrome, rheumatoid arthritis, scleroderma, or mixed connective tissue disease)

Myasthenia gravis

Unlike s-IBM, extraocular muscles are routinely involved; weakness is usually symmetric and tends to fluctuate, increasing with repeated or sustained exertion; spontaneous remissions can occur; motor unit action potentials (MUAPs) are unstable (increased jitter), whereas jitter is typically normal in s-IBM; repetitive nerve stimulation often shows abnormal decrement (rare in s-IBM); antibodies to acetylcholine receptors or muscle-specific kinase (MuSK) absent in s-IBM

Motor neuron disease

Upper motor neuron signs such as hyperreflexia and extensor plantar responses are not present in s-IBM; EMG in s-IBM may show neurogenic changes (ie, enlarged MUAPs), but these changes are relatively minor compared with predominance of smaller MUAPs, suggesting myopathy; fasciculation potentials are characteristic of motor neuron disease but rarely reported in s-IBM; recruitment is decreased in motor neuron disease and "early" in s-IBM; muscle biopsy in motor neuron disease shows denervation atrophy.

Acid maltase deficiency

Weakness is typically proximal-predominant (torso included); respiratory failure seen in about one third of adults; EMG is myopathic, similar to that of s-IBM, but in acid maltase deficiency, insertional activity is prominently increased, with profuse complex repetitive and myotonic discharges, whereas myotonic discharges are not seen in s-IBM and complex repetitive discharges are uncommon; muscle biopsy shows lysosomal (acid phosphatase-positive), glycogen-laden (PAS-positive) vacuoles, foci of acid phosphatase reactivity in nonvacuolated fibers, and glycogen accumulation by electron microscopy.

Chronic inflammatory demyelinating polyradiculoneuropathy

Weakness is usually both proximal and distal and mildly asymmetric, similar to s-IBM, but more often distally accentuated and lacking in the characteristic quadriceps/deep finger flexor emphasis of s-IBM; almost all patients have sensory signs and symptoms; examination shows diffuse hypo/areflexia; nerve conductions are abnormal, consistent with demyelination; EMG shows chronic reinnervational and no myopathic changes; serum creatine kinase (CK) is typically normal.

*Patients whose polymyositis does not respond to treatment and who have a clinical picture suggestive of s-IBM should be reevaluated. A repeat biopsy should be considered, as they may have s-IBM. Failure to confirm the diagnosis on initial biopsy may have been due to sampling error or insufficient processing.


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