[The role of skeletal muscle biopsy in the diagnosis of neuromuscular disorders]

Immunohistochemical and ultrastructural analysis of sporadic inclusion body myositis: a case series

Sporadic inclusion body myositis (s-IBM) is a progressive, skeletal muscle disease with poor prognosis. However, establishing the final diagnosis is difficult because of the lack of clear biomarkers in the blood serum and very slow development of clinical symptoms. Moreover, most other organs function normally without any disturbance. Here, in patients with this untreatable disease, we have underlined the importance of immunohistochemical and ultrastructural assessment of skeletal muscle in patients diagnosed with s-IBM. The goal of this study was to identify the distribution of specific antigens and to determine morphological features in order to localize pathological protein aggregates, rimmed vacuoles, and loss of myofibrils, which are key elements in the diagnosis of s-IBM. All studied patients were between 48 and 83 years of age and were hospitalized in the Department of Rheumatology and Internal Medicine between 2011 and 2016. Anamneses revealed an accelerated progression of muscle atrophy, weakness of limb muscles, and difficulties with climbing stairs. Based on histopathology and transmission electron microscopy examination, inflammatory infiltrations consisting of mononuclear cells, severe atrophy and focal necrosis of myofibers, splitting of myofilaments, myelinoid bodies and rimmed vacuoles were observed. Primary antibodies directed against CD3, CD8, CD68, cN1A, beta-amyloid, Tau protein and apolipoprotein B made it possible to identify types of cells within infiltrations as well as the protein deposits within myofibers. Using a combination of immunohistochemistry and electron microscopy methods, we were able to establish the correct final diagnosis and to implement a specific treatment to inhibit disease progression.

Nemaline myopathy in a newborn infant: a rare muscle disorder

Nemaline myopathy (NM) is a genetically and clinically heterogeneous muscle disorder, defined by the presence of characteristic nemaline bodies on muscle biopsy. The disease has a wide spectrum of phenotypes, ranging from forms with neonatal onset and fatal outcome to asymptomatic forms. The neonatal form is severe and usually fatal. The clinical variability, with differing age of onset and severity of symptoms makes the diagnosis difficult during infancy. There is no curative treatment. L-tyrosine may prevent aspiration by reducing pharyngeal secretions and drooling. Most of the patients die from respiratory and cardiac failure. This article discusses a newborn infant who presented with generalized weakness and respiratory failure. Partial response to L-tyrosine treatment was noted. The case is worth presenting to remind clinicians of congenital myopathies in the differential diagnosis of floppy infant during neonatal period and to emphasize the importance of muscle biopsy in diagnosis.

Muscle pathology in 31 patients with calpain 3 gene mutations

BACKGROUND AND PURPOSE

At present, more than 20 different forms of limb-girdle muscular dystrophies (LGMDs) are known (at least 7 autosomal dominant and 14 autosomal recessive). Although these different forms show some typical phenotypic characteristics, the existing clinical overlap makes their differential diagnosis difficult. Limb-girdle muscular dystrophy type 2 (LGMD2A) is the most prevalent LGMD in many European as well as Brazilian communities and is caused by mutations in the gene CAPN3. Laboratory testing, such as calpain immunohistochemistry and Western-blot analysis, is not totally reliable, since up to 20% of molecularly confirmed LGMD2A show normal content of calpain 3 and a third of LGMD2A biopsies have normal calpain 3 proteo-lytic activity in the muscle. Thus, genetic testing is considered as the only reliable diagnostic criterion in LGMD2A.

MATERIAL AND METHODS

In an attempt to find a correlation between genotype and muscle pathology in limb-girdle muscular dystrophy 2A we performed histopathological investigation of a group of 31 patients subdivided according to the type of pathologic CAPN3 gene mutation.

RESULTS

In all biopsies typical features of muscular dystrophy such as fiber necrosis and regeneration, variation in fiber size and fibrosis were noted. Lobulated fibers were often encountered in the muscle biopsies of LGMD2A patients. Such fibers were more frequent in patients with 550delA mutation.

CONCLUSIONS

These findings may be helpful in establishing diagnostic strategies in LGMD.

Stepwise approach to myopathy in systemic disease

Muscle diseases can constitute a large variety of both acquired and hereditary disorders. Myopathies in systemic disease results from several different disease processes including endocrine, inflammatory, paraneoplastic, infectious, drug- and toxin-induced, critical illness myopathy, metabolic, and myopathies with other systemic disorders. Patients with systemic myopathies often present acutely or sub acutely. On the other hand, familial myopathies or dystrophies generally present in a chronic fashion with exceptions of metabolic myopathies where symptoms on occasion can be precipitated acutely. Most of the inflammatory myopathies can have a chance association with malignant lesions; the incidence appears to be specifically increased only in patients with dermatomyositis. In dealing with myopathies associated with systemic illnesses, the focus will be on the acquired causes. Management is beyond the scope of this chapter. Prognosis is based upon the underlying cause and, most of the time, carries a good prognosis. In order to approach a patient with suspected myopathy from systemic disease, a stepwise approach is utilized.