Quiz Form

Question Date: 24/10/2023

Question: Which of these histological features is the most sensitive finding in dermatomyositis?

Options:

• Perivascular inflammation
• Perifascicular atrophy
• Expression of Interferon inducible proteins on muscle fibers and vessels
• Deposition of MAC on blood vessels

Correct Answer: Expression of Interferon inducible proteins on muscle fibers and vessels

Explaination: In dermatomyositis, the inflammation is located around blood vessels (perivascular inflammation) and is humoral than cell mediated. As a result, deposition of membrane attack complex (MAC) is seen on capillaries and small blood vessels. The characteristic histological feature is perifascicular atrophy (atrophy of fibers in the periphery of the muscle fascicle). Perifascicular atrophy is not seen in other myopathies. However it is not sensitive and may be seen in less than 50% of biopsies in dermatomyositis. Interferon type 1 leads to overexpression of proteins on muscle fibers and small blood vessels. Expression of one such protein, MxA (Myxoma virus resistance protein) is more sensitive than perifascicular atrophy or MAC deposition.

Reference: Doughty C T, Amato A A. Disorders of Skeletal Muscle. Bradley and Daroffs Neurology in Clinical Practice. 2022. Ch 1091978