Contributed by Jantima Tanboon, MD1, Akinori Uruha, MD, PhD2, Kohei Hamanaka, MD, PhD2, Juri Hasegawa, MD3, Ichizo Nishino, MD, PhD2
Department of 1Pathology, Siriraj Hospital, Mahidol, University, Bangkok, Thailand.
Departments of 2Genome Medicine Development, Medical Genome Center and Neuromuscular Research
National Institute of Neuroscience, National Center of Neurology and Psychiatry (NCNP), Tokyo, Japan.
Department of 3Neurology, Tomishiro Central Hospital Okinawa, Japan.
The patient was a 62-year-old woman who presented at the hospital with a one-month history of muscle pain and skin rash. Before this visit, she had experienced fever for 2 months. She had no other underlying medical condition except for rheumatoid arthritis which had been treated for over 20 years. Physical examination revealed mild symmetrical proximal muscle weakness of both upper and lower extremities (Medical Research Council grade 4). Erythema was observed in lower legs. Serum creatine kinase (CK) was 2048 U/L (normal range 32 - 180 U/L). Muscle biopsy was performed in the left tibialis anterior muscle.
On H&E (Figure 1a and Figure 1b), there is moderate fiber size variation ranging from 20-80 Ám. The perimysium is generally edematous and fragmented. Mild endomysial fibrosis is observed. Necrotic and regenerating fibers are common; most of them locate at perifascicular regions. Focal endomysial and perivascular lymphocytic infiltration is noted, but not surrounding or invading into non-necrotic fibers. Macrophages are associated with necrotic fibers. Fibers with internalized nuclei are present, 20%. There are no structural abnormalities such as ragged-red fibers, nemaline bodies, or rimmed vacuoles identified by modified Gomori Trichrome (not shown). The intermyofibrillar network demonstrated by NADH are well organized except for the necrotic and regenerating fibers (not shown). Alkaline phosphatase activity is seen in perimysium in addition to regenerating fibers (Figure 1c). There is no fiber type grouping demonstrated by ATPase stainings. Others stainings including acid phosphatase, COX, SDH, oil red O, PAS, NSE, and AChE show no additional abnormalities. Immunohistochemical study for HLA-DR shows scattered cytoplasmic positivity, especially in perifascicular regions (Figure 1d) while staining for myxovirus resistant protein A (MxA) is negative (not shown). What is your diagnosis?