Immune-Mediated Necrotizing Myopathy. IMNM O'Grady J, Harty L, Mayer N, Critcher V, Ryan J - J Clin Med Res (2015)  CC BY-2.0

Definition

IMNM is distinguished from other myositis types by muscle tissue (biopsy) from the muscle, most often taken from the thigh. Typically, the absence or near absence of inflammatory changes (inflammatory cells) in the tissue is present even if the cells are damaged and die (necrotic). IMNM is in some cases associated with statin treatment (against high cholesterol). anti-HMGCR is typically antibody

Symptoms

The disease picture is characterized by pronounced muscle weakness

Diagnosis

Blood tests

• Often very high blood counts for CK (creatine kinase which is a muscle enzyme)
• Antibodies may be present in the form of
  • anti-SRP
  • anti-HMGCR

Biopsy

• Typical changes (see above)

Treatment

• Often, IMNM responds poorly to drug treatment
• Testing: Rituximab (dose as in the treatment of rheumatoid arthritis). An alternative is immunoglobulins intravenously (IVIG) 2g / kg every 4. week. The dose can be distributed over 3 days (for example, a body weight of 60 kg will indicate IVIG 40g / day = 120g for a total of three days). If there is a risk of blood clots, Fragmin or similar preventive measures are given. Kidney function is controlled.

Association to other diseases

• Virus

  • IMNM is in some cases associated with viral infections (HIV, Hepatitis C)

• Cancer

  • Cancer diseases may exist in some cases

Statin-induced myosititis

• anti-HMGCR present in some

Other systemic connective tissue disorders

Literature

• Basharat P, 2015

Myositis, BINDEVEVSSYKDOMMER.no

• Bindevevssykdommer.no
• Vaskulitt.no