Necrotizing Myopathy Evaluation, Serum – Mayo Clinic Laboratories | Neurology Catalog

Necessary Information

Provide the following information:

-Relevant clinical information

-Ordering provider name, phone number, mailing address, and e-mail address

Specimen Required

Collection Container/Tube:

Preferred: Red top

Acceptable: Serum gel

Submission Container/Tube: Plastic vial

Specimen Volume: 3 mL

Collection Instructions: Centrifuge within 2 hours of collection and aliquot serum into a plastic vial.

Useful For

Evaluating patients with suspected necrotizing autoimmune myopathy

Profile Information

Test ID
Reporting Name
Available Separately
Always Performed

NSI1
Necrotizing Myopathy Interp, S
No
Yes

HMGCR
HMG-CoA Reductase Ab, S
Yes
Yes

SRPIS
SRP IFA Screen, S
No
Yes

Testing Algorithm

This focused algorithmic test is designed to achieve high sensitivity for identification of antibodies specific for necrotizing autoimmune myopathy (HMGCOA-IgG and SRP-IgG). This test is unique in the market by having an initial screen for signal recognition particle (SRP) antibodies performed using tissue indirect immunofluorescence, which increases clinical sensitivity as compared to SRP immunoblot methodologies.

If indirect immunofluorescence assay (IFA) pattern suggests signal recognition particle (SRP) antibody, SRP IFA titer and SRP54 immunoblot are performed at an additional charge.

For more information, see Necrotizing Myopathy Evaluation Algorithm

Method Name

SRPIS, SRPTS: Indirect Immunofluorescence Assay (IFA)

SRPBS: Immunoblot

HMGCR: Chemiluminescent Assay (CIA)

NSI1: Medical Interpretation

Reporting Name

Necrotizing Myopathy Evaluation, S

Specimen Type

Serum

Specimen Minimum Volume

2 mL

Specimen Stability Information

Specimen Type
Temperature
Time
Special Container

Serum
Refrigerated (preferred)
28 days

 
Frozen 
28 days

 
Ambient 
72 hours

Clinical Information

Necrotizing autoimmune myopathy (NAM) is a serious, but rare muscle disease strongly associated with autoantibodies to either signal recognition protein (SRP) or 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR).(1) NAM typically manifests with subacute proximal limb muscle weakness and persistently elevated serum creatine kinase (CK) concentrations, but slower onsets can occur and complicate diagnosis. Muscle biopsies in affected patients can demonstrate necrotic and regenerating myofibers without inflammatory infiltrates, suggesting the diagnosis.(2) However, sampling issues and lack of access to persons having expertise in obtaining, preparing, and interpreting muscle biopsy specimens may delay a diagnosis.(3)

Early identification of NAM and subsequent aggressive immune-modulating therapy is critical.(1,3) Discovery of SRP- or HMGCR–IgG autoantibodies can aid in establishing an earlier diagnosis and treatment initiation. In addition, the discovery of SRP or HMGCR autoantibodies should prompt a search for an underlying malignancy.(4) Serial testing for these autoantibodies can delay diagnosis with the discovery of either antibody aiding in establishing an earlier diagnosis and treatment initiation.(1,3)

The clinical onsets are not specific to NAM consisting of proximal limb weakness in associations with an elevated serum creatinine kinase, with or without exposure to lipid lowering statin medications.(1,3-9) The clinical presentation can be confused with forms of inflammatory (dermatomyositis, polymyositis), toxic, metabolic or even neurodegeneration (ie, muscular dystrophy) and the diagnosis delayed without serological testing by SRP- or HMGCR-autoantibody testing. Panel testing of both HMGCR and SRP autoantibodies is the preferred strategy for the best patient care.

Reference Values

3-Hydroxy-3-Methylglutaryl Coenzyme-A (HMG-CoA) Reductase:

<20.0 CU

Signal Recognition Particle Antibody Screen:

Negative

Signal Recognition Particle Antibody:

Negative

Signal Recognition Particle Antibody, Titer:

<1:240

Interpretation

Seropositivity for 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) or signal recognition protein (SRP) autoantibodies supports the clinical diagnosis of necrotizing autoimmune myopathy (NAM). A paraneoplastic basis should be considered, according to age, sex, and other risk factors. In cases of NAM, immune therapy is required and often multiple simultaneously utilized immunotherapies are needed to successfully treat patients.

Clinical Reference

1. Kassardjian CD, Lennon VA, Alfugham NB, et al: Clinical Features and Treatment Outcomes of Necrotizing Autoimmune Myopathy. JAMA Neurol 2015 Sep;72(9):996-1003

2. Emslie-Smith A M, Engel A G: Necrotizing myopathy with pipestem capillaries, microvascular deposition of the complement membrane attack complex (MAC), and minimal cellular infiltration. Neurology 1991;41(6):936-939

3. Ramanathan S, Langguth D, Hardy T, et al: Clinical course and treatment of anti-HMGCR antibody-associated necrotizing autoimmune myopathy. Neurol Neuroimmunol Neuroinflamm 2015 June;2(3):e96

4. Allenbach Y, Keraen J, Bouvier AM, et al: High risk of cancer in autoimmune necrotizing myopathies: usefulness of myositis specific antibody. Brain 2016 Aug;139(Pt 8):2131-2135

5. Christopher-Stine L, Casciola-Rosen L, Hong G, et al: A novel autoantibody recognizing 200-kd and 100-kd proteins is associated with an immune-mediated necrotizing myopathy. Arthritis Rheum 2010 May;62(9):2757-2766

6. Mammen AL, Chung T, Christopher-Stine L, et al: Autoantibodies against 3-hydroxy-3-methylglutaryl-coenzyme A reductase in patients with statin-associated autoimmune myopathy. Arthritis Rheum 2011 Mar;63(3):713-721

7. Hengstman GJ, ter Laak HJ, Vree Egberts WT, et al: Anti-signal recognition particle autoantibodies: marker of a necrotising myopathy. Ann Rheum Dis 2006;65(12):1635-1638

8. Miller T, Al-Lozi MT, Lopate G, Pestronk A: Myopathy with antibodies to the signal recognition particle: clinical and pathological features. J Neurol Neurosurg Psychiatry 2002 Oct;73(4):420-428

9. Watanabe Y, Uruha A, Suzuki S, et al: Clinical features and prognosis in anti-SRP and anti-HMGCR necrotising myopathy. J Neurol Neurosurg Psychiatry 2016 Oct;87(10):1038-1044

Day(s) Performed

Tuesday, Thursday

Report Available

10 to 14 days

Test Classification

This test was developed, and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.

CPT Code Information

86255

82397

86256 (if appropriate)

84182 (if appropriate)

LOINC Code Information

Test ID
Test Order Name
Order LOINC Value

NMS1
Necrotizing Myopathy Evaluation, S
97561-5

Result ID
Test Result Name
Result LOINC Value

607414
HMG-CoA Reductase Ab, S
93493-5

603543
Necrotizing Myopathy Interp, S
69048-7

603540
SRP IFA Screen, S
97562-3

Reflex Tests

Test ID
Reporting Name
Available Separately
Always Performed

SRPBS
SRP Immunoblot, S
No
No

SRPTS
SRP IFA Titer, S
No
No

Forms

If not ordering electronically, complete, print, and send a Neurology Specialty Testing Client Test Request (T732) with the specimen.

Special Instructions

• Necrotizing Myopathy Evaluation Algorithm