Bethlem myopathy is a slowly progressive muscle disease characterized predominantly by contractures, rigidity of the spine, skin abnormalities and proximal muscle weakness. Symptoms may present as early as infancy, with typical contractures and hyperlaxity of joints; however, in some patients, symptoms may go unnoticed until adolescence or adulthood.
Bethlem myopathy 1 (Collagen VI genes)
See Bethlem myopathy 1 Clinical synopsis on OMIM: 158810 In Bethlem myopathy 1, in the calf, one of the first signs is often a 'rim' of
fatty infiltration between the soleus and gastrocnemius muscles. Although there is fatty infiltration, the calf muscles do not appear pseudohypertrophic, in fact they may appear slender. In the thighs, there is also significant fatty infiltration of the vasti muscles, with a rim of fatty infiltration on the periphery of the muscles, while the center is more or less spared (characteristic "outside-in" pattern). This "outside-in" pattern distinguishes it from other myopathies known to have contractures, such as Emery-Dreifuss muscular dystrophy. Contractures presenting in infancy may resolve by age 2 years, but reoccur as the disease progresses, typically by late of the first decade or early teens.
Bethlem myopathy 2 (Collagen XII gene)
See Bethlem myopathy 2 Clinical synopsis on OMIM: 616471 In Bethlem myopathy 2, there is phenotypic variability. In one family, the only notable finding on
T1-weighted MR images (used to detect fatty infiltration) was atrophy of the rectus femoris muscles of the thigh, with the degree of atrophy matching the severity of the disease, but no fatty infiltration. In another family, only the more severely affected older patient showed significant abnormality, by having symmetrical
fatty atrophy of the femoral quadriceps of the thigh, the adductor and medial gastrocnemius muscles of the calf; as well as asymmetrical fatty atrophy of the adductor longus of the thigh. No muscle hypertrophy was reported and the muscles of the patients without fatty atrophy appeared normal. Bethlem myopathy 2 also differs by including the possibility of
scapula winging,
pectus excavatum, stooped posture,
kyphosis (hunchback),
micrognathia,
retrognathia, and a
high-arched palate. Childhood
muscle weakness improves in teen years, but muscle weakness returns by the third decade of life. ==Diagnosis==