Limb-Girdle Muscular Dystrophy Workup

Updated: Aug 15, 2019
  • Author: Monica Saini, MD, MBBS; Chief Editor: Nicholas Lorenzo, MD, MHA, CPE  more...
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Workup

Laboratory Studies

Creatine kinase testing aids diagnosis.

  • Autosomal recessive limb-girdle muscular dystrophies (LGMDs) often cause extremely high CK levels. The sarcoglycanopathies (LGMD2C-2F) and LGMD2B markedly elevate CK levels by 10-150 times normal. The other autosomal recessive LGMDs usually cause CK elevations that are 3-80 times normal.

  • Autosomal dominant LGMD1C can result in high CK elevations of 5-25 times normal. All other autosomal dominant LGMDs result in CK levels between normal and 15 times normal.

  • Myofibrillar myopathies have CK levels ranging from normal to 7 times normal.

  • Consider other myopathies that markedly elevate CK levels: dystrophinopathies, dermatomyositis and/or polymyositis, hypothyroid myopathy, rhabdomyolysis, and acid maltase deficiency.

A guideline for the diagnosis and management of patients with limb-girdle or distal muscular dystrophies, issued by the American Academy of Neurology and the American Association of Neuromuscular & Electrodiagnostic Medicine, calls for referral of patients suspected of having MD to a specialist center for evaluation and genetic testing. The guideline provides algorithms for diagnosis based on the clinical phenotype, including pattern of muscle involvement, inheritance pattern, age of onset, and associated manifestations (e.g. contractures, cardiomyopathy, respiratory failure).  If initial targeted genetic testing (either single gene or a panel of LGMDs) is negative, a muslce biopsy showld be obtained to look at the immunohistochemical staining patterns using antibodies directed at known disease associated proteins (e.g. dystrophin, sarcoglycans, merosin, α-dystroglycan, dysferlin, cveloin-3, etc) and to look for distinguishing features (e.g. rimmed vacuoles, myofibrillar myopathy).  If subsequent targeted genetic testing remains negative then whole exome sequncing should be performed. [64, 65]

Next‐generation sequencing (NGS)‐based gene‐panel testing, using targeted NGS panel, is now available for the diagnosis of LGMD. Whole genome sequencing has additional benefits of identifying novel pathogenic mutations and putative phenotype-influencing variants, as well as identifying potential digenic or multigenic contribution to LGMD especially in patients with atypical presentations and /or progression. [66, 67]

In a large cohort of LGMD families [68] 35% were diagnosed based on protein-based testing (muslce biopsy) followed by targeted candidate gene testing.  Of the remaining patients, 60 families underwent whole exome sequencing, pathogenic mutations in known myopathy genes were identified in 45% of the families.  Interestingly, about half of the identified genes were not LGMD genes, highlighting the clinical overlap between LGMD and other myopathies.  Common causes of phenotypic overlap included genes causing collagen myopathy, metabolic myopathies and congenital myopathies.           

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Imaging Studies

Magnetic resonance imaging (MRI) can help differentiate forms of LGMD. Hyperintense signal change on T1 scans is seen in more severely affected muscles. An MRI study of 20 patients with LGMD showed the following:

  • Patients with LGMD2A show prominent involvement of thigh adductors, hamstrings, and medial head of the gastrocnemius, with sparing of the sartorius. Serial imaging shows stronger deterioration in the soleus muscle, vastus intermedius, and biceps femoris. [69]

  • Patients with LGMD2B can have a variable MRI picture. The adductor magnus, quadriceps, and calf muscles are predominantly involved, with relative sparing of the Sartorius and gracilis muscles. [70] Involvement of gastrocnemius predominates in Miyoshi myopathy, and involvement of glutei and anterior and posterior thigh muscle is prominent in patients with a LGMD phenotype. Tibialis anterior and axial abnormalities are described in patients with anterior tibial myopathy and axial myopathy, respectively.

  • Patients with sarcoglycanopathies do not show any major differences regarding pattern of muscle involvement, as seen on MRI. Adductor and glutei muscles seem to be the first affected, with a proximodistal gradient evident in the vastus lateralis. Adductor longus may show some areas of sparing, with a complete or relative sparing of tibialis posterior and flexor digitorum longus. Less consistently, a relative hypertrophy of either sartorius or gracilis may be seen. [71]

  • Patients with LGMD2D and with Becker muscular dystrophy had more severe MRI changes in the anterior thigh compartment than in the posterior thigh.

  • Muscle tissue in patients with LGMD2I who have the founder mutation c.545A>G in FKRP shows a distinctive concentric pattern of fatty infiltration and edema on MRI, most pronounced in the vastus intermedius and vastus medialis muscles around the distal femoral diaphysis. [72]

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Other Tests

Needle electromyography (EMG) and nerve conduction studies (NCSs)

Order EMG and NCSs in all patients with suspected LGMD to confirm the myopathic nature of the disease.

NCS results are normal in LGMD.

EMG shows early recruitment and the typical small-amplitude, narrow-duration, polyphasic motor-unit potentials that are seen in muscular diseases.

Abnormal spontaneous activity in the form of fibrillations and positive sharp waves is not prominent but has been described in a few cases of LGMD. When present, it should raise the clinician's suspicion for an inflammatory myopathy, such as polymyositis.

Myotonic or pseudomyotonic discharges may occasionally be noted in LGMD1A, LGMD1D, and LGMD1E.

Electrocardiography

Cardiac involvement is common in the autosomal dominant syndromes of LGMD1A and 1B (50%–65%). Cardiomyopathy and cardiac arrhythmias in LGMD1B may cause clinically significant morbidity. In patients with LGMD1E (dilated cardiomyopathy with conduction defect and muscular dystrophy), cardiomyopathy and arrhythmias are nearly always present.

In the autosomal recessive LGMD syndromes, cardiomyopathy is uncommon except in LGMD2G and 2I, where as many as 30%–50% of patients can have mild-to-moderate cardiomyopathy. In the sarcoglycanopathies (most often LGMD2E and 2F), cardiomyopathy is occasionally problematic.

In myofibrillar myopathies, cardiac disease is common, occurring in more than 50% of cases. Presentation can be with cardiomyopathy or cardiac conduction disturbances.

Annual screening with ECG (and possibly echocardiography if the patient is symptomatic) is important for quick diagnosis and follow-up in cases of LGMD and myofibrillar myopathy with cardiac disease.

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Procedures

Muscle biopsy is the most important diagnostic evaluation of patients in whom LGMD is suspected.

In most cases of LGMD, routine histochemical studies show typical dystrophic features, including various degrees of muscle-fiber degeneration and regeneration, variation in fiber size with small round fibers, and endomysial fibrosis.

Details of routine muscle histochemistry include the following:

  • In LGMD1A the muscle biopsy may show rimmed vacuoles.

  • In LGMD1C the muscle biopsy may show only mild myopathic features.

  • In LGMD2B the biopsy may show perimysial and perivascular T-cell infiltrates and upregulation of major histocompatibility complex (MHC-1), and may be mistaken for polymyositis.

  • In LGMD2G there may be rimmed vacuoles.

  • In LGMD2H the biopsy may show features of sarcotubular myopathy (see Congenital myopathy).

  • In LGMD2J the muscle biopsy may be myopathic with rimmed vacuoles.

Immunohistochemical findings are as follows:

  • Dystrophin testing is usually the first step in dystrophic biopsy performed by using antibodies against the N-terminus, rod, and C-terminus. A minor reduction in dystrophin staining can be seen in sarcoglycanopathies. Conversely, a minor reduction in sarcoglycan staining may occur in dystrophinopathies.

  • All sarcoglycan antibodies should be tested next. While the pattern of sarcoglycan deficiency can be quite variable in sarcoglycanopathies, some generalizations can be made. [73] If α-sarcoglycan and γ-sarcoglycan are both absent, there is frequently a mutation in α-sarcoglycan (LGMD2D). Patients with a γ-sarcoglycan mutation (LGMD2C) have complete absence of γ-sarcoglycan. Patients with reduced levels of γ-sarcoglycan usually have a mutation in α-sarcoglycan (LGMD2D) or less commonly of β-sarcoglycan (LGMD2E).

  • Antibodies to dysferlin and calpain-3 are also important in evaluating LGMDs. Patients with LGMD2A have reduced staining for calpain-3 by Western blot. Reduction or loss of staining for the 60kD band is more sensitive and specific than loss of staining for the 30kD band. Loss of staining for both bands occurs in about 25% of cases and is highly specific for a calpain-3 mutation. About 25% of patients with a mutation may have a normal Western blot. Patients with LGMD2A may have reduction in immunohistochemical staining for dysferlin. Staining for dystrophin and the sarcoglycans is normal. Calpain-3 staining may be reduced in other disorders including LGMD1C, LGMD2B, LGMD2I, LGMDJ, and dystrophinopathies.

  • Patients with LGMD2B have reduced or absent immunohistochemical staining for dysferlin as well as absent or reduced Western blot staining. Absence of staining is highly specific for a mutation in the dysferlin gene, but there is no correlation between the level of staining and the severity of disease. However, a mutation in dysferlin was always found in patients with reduction in Western blot staining to less than 20% of normal. [74] Calpain-3 staining may also be reduced. Dystrophin and sarcoglycan staining is normal.

  • Patients with LGMDI, LGMD2K and LGMD2M all have reduced staining for glycosylated α-dystroglycan. There may also be a reduction in staining for laminin-α2.

  • Patients with LGMD1A often have increased staining for myotilin, desmin, and for other proteins typically found in myofibrillar myopathies (see below).

  • Patients with LGMD1C have reduced staining for caveolin-3 by immunohistochemistry and Western blot. There may also be reduced staining for dysferlin on immunohistochemistry.

  • Myofibrillar myopathies

    • General features include myopathic changes as well as the presence of hyaline/cytoplasmic bodies.

    • Immunohistochemistry shows aggregates containing desmin as well as numerous other proteins (myotilin, laminin-B, ubiquitin, αβ-crystallin, β-amyloid, dystrophin).

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Histologic Findings

Examples of histologic findings are depicted in the images below.

Top: Photomicrograph shows normal alpha-sarcoglyca Top: Photomicrograph shows normal alpha-sarcoglycan staining of a myopathic biopsy specimen. Note dark staining around the rims of the muscle fibers. Bottom: Alpha-sarcoglycan stain of a muscle biopsy specimen from a patient with alpha-sarcoglycan deficiency. Note the absence of staining at the rims of the muscle fibers. Patterns of staining similar to these are observed in all the sarcoglycanopathies, dysferlinopathy, calpainopathy and limb-girdle muscular dystrophy type 2I (LGMD2I, Fukutin-related proteinopathy). However, staining may be variably reduced or absent.
Gomori trichrome–stained section in patient with m Gomori trichrome–stained section in patient with myofibrillar myopathy. Note the abnormal accumulations of blue-red material in several muscle fibers.
Immunohistochemical staining by using an anti-desm Immunohistochemical staining by using an anti-desmin antibody in a patient with a myofibrillar myopathy. Courtesy of Alan Pestronk.
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