AANEM Connect

Dear Colleagues,
I am hoping to enlist your expertise in a case that is perplexing me.

23 yo M admitted for focal swelling of left forearm and pigmenturia. He had done some light upper body resistance exercises 3 days prior (10 lb dumbbells) and was sore following this. CK on admission was 14,000. MRI left forearm showed edema and enhancement in the left brachioradialis muscle only. He was hydrated and his CK came down slowly to 700 over the next week. He did not receive steroids. About 2 weeks prior to admission, his PCP noted elevated AST/ALT to 75/91 (his GGT was later normal). 

I saw him 1 week after discharge. His CK at that point was 106.There was some loss of bulk in the left brachioradialis and very mild weakness of elbow flexion, but the remainder of the exam was normal. His HMGCR antibody (ARUP) was positive at 49 (normal <20). The ARUP extended myositis antibody panel was negative. 

He is scheduled to get a muscle biopsy to see if he has changes consistent with necrotizing myopathy, then EMG to assess other muscles for subclinical abnormalities. Will recheck HMGCR antibody in about 3 months. 

After searching the literature, I found only one case report of immune mediated necrotizing myopathy presenting focally like this. I'm not sure which is more likely - an atypical presentation of a rare disease or a false positive antibody despite a reportedly very high specificity. 

My questions for this community:
1. Has anyone seen this before? Is focal-onset IMNM a reasonable conclusion?
2. If CK has returned to normal but the affected muscle remains weak, does that justify treatment with steroids? How aggressively would you treat this?
3. What kind of exercise restrictions would you recommend, if any?

Your expertise, as always, is highly valued!
Dan Simmons