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October 15, 2021

Mycobacterial Infection

Mycobacterial Infection

Hematoxylin and eosin FFPE 100x original magnification

Mycobacterial Infection

Hematoxylin and eosin FFPE 100x original magnification

 

Mycobacterial Infection

Acid Fast Stain (Kinyoun) FFPE 1000x oil immersion

 

This 45-year-old patient presented to the emergency department with left thigh and buttock pain of four months’ duration, and two weeks of fever (105oF) and chills. The patient’s past medical history is significant for autoantibody-positive rheumatoid arthritis treated with mycophenolate mofetil and steroid, and recent findings of focal central disc herniation at L5-S1. The patient is reported to have traveled to Asia and India. Chest X-ray showed mild bibasilar atelectasis. MRI showed avascular necrosis of the left femoral head, edema, and enhancement throughout the left proximal thigh and gluteal muscles. Laboratory studies showed normal CPK, elevated CRP, peripheral blood leukocytosis with left shift, negative blood culture, and COVID-19 PCR. During muscle biopsy, some “clumpy purulent grumous-type” material was found within the gluteal muscles. Tissue was obtained for pathologic evaluation (see following 3 images) and tissue culture.

Which of the following is the best final diagnosis based on the images?

A. Sarcoidosis

B. Granulomatous myositis

C. Vasculitis

D. Mycobacterial infection

 

Answer: Mycobacterial infection

Mycobacterial infection is the most correct answer to this question. Note that the granulomata, in this case, were noncaseating. Further classification of the mycobacterial organisms is pending.

Granulomatous inflammation of skeletal muscle is relatively uncommon and is designated under the umbrella term of “granulomatous myositis”. Granulomatous inflammation involving skeletal muscle has multiple causes, including mycobacterial infection. Involvement of skeletal muscle by sarcoidosis (so-called “sarcoid myopathy”) is the most common cause of granulomatous myositis.

This case is a nice demonstration that the diagnosis of sarcoidosis requires ruling out other causes of granulomatous myositis (i.e. sarcoidosis is a diagnosis of exclusion). Granulomatous inflammation may be a component of vasculitis. However, no involvement of blood vessels is present in the images provided for this case.

References

Prayson RA. Granulomatous myositis. Clinicopathologic study of 12 cases. Am J Clin Pathol. 1999 Jul;112(1):63-8. doi: 10.1093/ajcp/112.1.63. PMID: 10396287.

Le Roux K, Streichenberger N, Vial C, Petiot P, Feasson L, Bouhour F, Ninet J, Lachenal F, Broussolle C, Sève P. Granulomatous myositis: a clinical study of thirteen cases. Muscle Nerve. 2007 Feb;35(2):171-7. doi: 10.1002/mus.20683. PMID: 17068767.

Le Roux K, Streichenberger N, Vial C, Petiot P, Feasson L, Bouhour F, Ninet J, Lachenal F, Broussolle C, Sève P. Granulomatous myositis: a clinical study of thirteen cases. Muscle Nerve. 2007 Feb;35(2):171-7. doi: 10.1002/mus.20683. PMID: 17068767.

Shipman AR, Levell NJ, Afridi KS, et al. Disseminated Mycobacterium avium infection masquerading as longstanding polymyositis. JRSM Short Rep. 2011;2(12):94. doi:10.1258/shorts.2011.011091