Muscle
Muscular dystrophies
Becker muscular dystrophy

Author: Wesley Hiser, M.D.
Editor: Jesse L. Kresak, M.D.

Revised: 29 January 2018, last major update January 2018

Copyright: (c) 2002-2018, PathologyOutlines.com, Inc.

PubMed Search: Becker muscular dystrophy [title] "loattrfree full text"[sb]

Cite this page: Hiser, W. Becker muscular dystrophy. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/musclebeckermusculardystrophy.html. Accessed February 25th, 2018.
Definition / general
  • Muscular dystrophy caused by dystrophin (DMD) gene mutations on chromosome Xp21, leading to decreased / altered dystrophin protein expression
  • Variable clinical course but progressive proximal weakness typically begins in childhood and leads to loss of ambulation in early adulthood
Essential features
  • Closely related to Duchenne muscular dystrophy (DMD), in which dystrophin mutations lead to complete or near complete absence of dystrophin protein expression
  • Mutations in Becker muscular dystrophy (BMD) lead to a truncated dystrophin protein with differing degrees of functionality and expression
  • Histologic findings similar to DMD with myofiber size variation, nonspecific myofiber regenerative changes and fibrosis / fatty replacement late in the disease course
Terminology
  • Named for the German physician, Peter Emil Becker, who first described the entity in the 1950's
  • The term "dystrophinopathy" refers to both Duchenne and Becker muscular dystrophies
ICD-10 coding
  • G71.0: muscular distrophy
Epidemiology
Sites
Pathophysiology
  • Mutations in the DMD gene lead to reduced production of a truncated dystrophin protein which maintains partial functionality
  • Dystrophin is a structural protein involved in linking the cytoskeleton with the extracellular matrix (Pediatr Clin North Am 2015;62:723)
Etiology
Clinical features
  • Significant variation in clinical presentation but patients typically present with muscle weakness during childhood
  • About half of patients exhibit muscle weakness by the age of 10 (Pediatr Clin North Am 2015;62:723)
  • Muscle weakness is most prominent proximally, typically in a limb girdle distribution
  • Ability to jump may be preserved in some patients
  • Cramping with strenuous physical activity
  • Ambulation typically lost by third decade but may be retained far into adulthood (Pediatr Clin North Am 2015;62:723)
  • Pseudohypertrophy of calf muscles
  • Cardiomyopathies common
  • Intellectual impairment is not typically seen
  • Women who are carriers usually do not exhibit symptoms but may be susceptible to cardiomyopathies
Diagnosis
  • Relies on clinical features in combination with genetic testing
  • Muscle biopsy is less frequently performed but is useful for assessment of dystrophin expression (Pediatr Clin North Am 2015;62:723)
Laboratory
  • Creatine kinase (CK) is significantly elevated but not to the degree seen in DMD
  • Peak CK levels are usually found around 10 - 15 years of age
  • ALT / AST may be elevated
  • Can see occasional myoglobinuria following strenuous activity (Pediatr Clin North Am 2015;62:723)
Prognostic factors
  • Extremely variable prognosis
  • Some patients have course similar to DMD, while others experience only mild muscle weakness without significant loss of function
Case reports
  • 9 year old boy with Becker muscular dystrophy with epilepsy and dysgnosia induced by duplication mutation of Dystrophin gene (BMC Neurol 2016;16:255)
  • 13 year old boy with a mutation in DMD causing Becker muscular dystrophy associated with intellectual disability (J Dev Behav Pediatr 2016;37:239)
  • 18 year old man with a case of Becker muscular dystrophy with early manifestation of cardiomyopathy (Korean J Pediatr 2012;55:350)
  • 26 year old man with a case of refractory heart failure in Becker muscular dystrophy improved with corticosteroid therapy (Int Heart J 2016;57:640)
Treatment
  • No curative treatment
  • Supportive therapy including intense physical therapy
  • Corticosteroids may be used in severe cases of BMD to improve muscle function and strength and may reduce scoliosis and severe cardiorespiratory complications
  • Numerous clinical trials for gene therapy are currently in progress
Microscopic (histologic) description
  • Typically less severe histologic findings than those seen in DMD
  • Variation in myofiber size with small, atrophic fibers and large, rounded fibers
  • Myofiber splitting with necrosis, phagocytosis and regeneration
  • Increased internal nuclei - nonspecific finding seen in a number of myopathic processes; healthy muscle typically shows no more than 3 - 5% of fibers with internal nuclei
  • Endomysial fibrosis and fatty replacement of muscle later in disease course
  • Inflammation (T cells, macrophages) may be seen in association with myofiber necrosis (Yachnis: Neuropathology - a Volume in the High Yield Pathology, 1st Edition, 2014)
Microscopic (histologic) images

Images hosted on PathOut server:

Images contributed by Wesley Hiser, M.D.

Myopathic features

Becker dystrophin IHC

​Intact dystrophin IHC

Spectrin control

Positive stains
  • Three antibodies which recognize epitopes in different domains are used to assess dystrophin expression (N-terminus, C-terminus and central rod domain)
  • Sarcolemmal expression of dystrophin will be altered or reduced in BMD
  • Spectrin is used as a control for assessing sarcolemmal membrane integrity (Yachnis: Neuropathology - a Volume in the High Yield Pathology, 1st Edition, 2014)
  • NADH and SDH oxidative stains may show nonspecific myofibrillar changes such as moth eaten or whorled fibers
Negative stains
  • Altered dystrophin expression may lead to absent staining for one or two dystrophin domains
Molecular / cytogenetics description
  • Mutation of the dystrophin (DMD) gene on chromosome Xp21
  • Mutations are in frame and do not shift the reading frame, resulting in internal deletions and duplications
  • Stop codon is not produced as in Duchenne muscular dystrophy, so dystrophin protein is still produced (Pediatr Clin North Am 2015;62:723)
  • Clinical features correlate with the functionality and amount of dystrophin
Differential diagnosis
Board review question #1
Mutations in what gene are responsible for Becker muscular dystrophy?

  1. BKR
  2. DMD
  3. MTM1
  4. NEB
  5. RYR1
Board review answer #1
B. DMD