Chronic myopathy due to immunoglobulin light chain amyloidosis

Abstract

Amyloid myopathy associated with a plasma cell dyscrasia is a rare cause of muscle hypertrophy. It can be a challenging diagnosis, since pathological findings are often elusive. In addition, the mechanism by which immunoglobulin light-chain deposition stimulates muscle overgrowth remains poorly understood. We present a 53–year old female with a 10-year history of progressive generalized muscle overgrowth. Congo-red staining and immunohistochemistry revealed perivascular lambda light chain amyloid deposits, apparent only in a second muscle biopsy. The numbers of central nuclei and satellite cells were increased, suggesting enhanced muscle progenitor cell formation. Despite the chronicity of the light chain disease, the patient showed complete resolution of hematologic findings and significant improvement of her muscle symptoms following autologous bone marrow transplantation. This case highlights the importance of early diagnosis and therapy for this treatable cause of a chronic myopathy with muscle hypertrophy.

A comparison study of prabotulinumtoxinA vs onabotulinumtoxinA in myostatin‐deficient mice with muscle hypertrophy

“…Muscle hyperplasia in MSTN‐deficient mice increased axon diameter and myelin thickness in the fore‐ and hindlimbs without affecting internode length . Consistently, it has been reported previously that generalized muscle hypertrophy decreases nerve conduction, the structural changes underlying this decrease can be observed histologically . These data indicate that the nerve conduction is not increased in proportion to skeletal muscle mass in adult Mstn −/− mice.…”

“…Specifically, Mstn −/− mice have heavier skeletal muscle, lower total adiposity and increased myofibre cross‐sectional area in the soleus and gastrocnemius . Additionally, generalized muscle hypertrophy has decreased nerve conduction; the structural changes underlying this decrease can be observed histologically . Our findings are consistent with the results of previous studies.…”

Secondary myopathy due to systemic diseases

“…Muscle involvement is frequent in amyloidosis and manifests as amyloid myopathy , clinically characterized by muscle hypertrophy (muscle overgrowth), or weakness. Depending on the cause of amyloidosis, different types of amyloid (AA, AL) may be produced.…”

“…Amyloidosis usually manifests systemically in all muscles but occasionally only a single muscle or a few muscles is/are affected . Amyloidosis is characterized by extracellular and perivascular deposition of AA or AL amyloid . Rarely, amyloid myopathy occurs in patients with hereditary transthyretin amyloidosis (ATTR) .…”

Muscle Hypertrophy in a Patient with Immunoglobulin D Multiple Myeloma

“…4 Differential diagnoses of diffuse skeletal muscle hypertrophy include hypothyroidism and a few neuromuscular disorders such as muscular dystrophies and nondystrophic myotonic disorders. 5 Unlike these diseases, serum CK is often normal in patients with amyloidosis. 6 It is important to consider amyloidosis, in particular when serum CK is not elevated, for the patients whose muscles are hypertrophic without exercise.…”