Muscle infection in chronic hepatitis B

M. Capasso 1, A. Di Muzio1, M. Comar2, C. Campello2, I. Robuffo3, A. Gambi4, MV De Angelis1,
A. Uncini1
Center for Neuromuscular Diseases and 4 Section of Clinical Pathology, Department of Oncology
and Neuroscience, University “G. d’Annunzio”, Chieti
UCO Institute of Hygiene, University of Trieste-Burlo Garofolo, Trieste
CNR, Institute of Organ Transplant and Immunocitology, Section of Chieti
Myopathies have been reported in the course of some viral illnesses, including few cases associated
with hepatitis B. However, as infection of muscle fibers has never convincingly demonstrated, the
muscle is commonly considered resistant to viral infection, and the occurrence of these myopathies
has been regarded as fortuitous or due to indirect immunological mechanisms.
We studied two patients with chronic hepatitis B and an asymptomatic or paucisymptomatic
myopathy, whose cause had not been found in spite of careful investigations.
Muscle biopsy showed mild necrosis and scanty inflammation in both. Through extractive and insitu polymerase-chain-reaction (PCR), immunohistochemistry, and immunoelectron microscopy,
we found HBV DNA and antigens inside muscle fibers. These fibers were usually structurally intact
and expressed major histocompatibility complex class I antigens (MHC-I), which is not expressed
normally and make infected fibers a possible target for immune response. Actually, in mice models
of DNA vaccination, intramuscular injection of HBsAg-encoding genes leads to muscle expression
of HBsAg and immune-mediate necrosis.
We think our findings demonstrate that HBV can infect muscle fibers and was probably responsible
for muscle injury in the patients we report. The possible direct involvement of the muscle in viral
infections should be reconsidered.