Immune-mediated necrotizing myopathy calculator

Shahar Shelly, M.D., and Christopher J. Klein, M.D., present:

Data entry for probability calculation of immune-mediated necrotizing myopathy (IMNM)

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Criteria
Symptoms
1
Myotonic discharges
2
Any statin exposure
3
Deltoid weakness
4
Gluteus maximus weakness
5
Finger flexor > finger extensor weakness (with equal weakness or without weakness score 'no')
6
Finger extensor > finger flexor weakness (with equal weakness or without weakness score 'no')
7
Ankle dorsi-flexor weakness
8
Creatine kinase > 1000 U/L

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Probability result

The following represents the probability of IMNM using a statistical algorithm. Percentages above 75% indicate patients who are highly likely to have IMNM, but clinical correlation with serological testing (HMGCR-IgG and SRP54-IgG), muscle biopsy, and temporal course are essential with rapid onsets less than 48 hours more typical for other forms of rhabdomyolysis.

* Triplett J, Shelly S, Livne G, et al. Diagnostic modeling and therapeutic monitoring of immune-mediated necrotizing myopathy: Role of electrical myotonia. Brain Commun. 2020 Dec 13;2(2):fcaa191.
** Allenbach Y, Mammen A, Benveniste O, Stenzel W; Immune-Mediated Necrotizing Myopathies Working Group. Clinico-sero-pathological classification of immune-mediated necrotizing myopathies. Neuromuscul Disord. 2018 Jan;28(1):87-99.