Case Review: MRI Leads to Non-Rheumatic Diagnosis Surprise

Muscle disease in anorexia nervosa is seen mainly in cases of severe weight loss. Initially, patients lose mostly adipose tissue, but with progressive weight loss, muscle mass is also affected, leading to proximal muscle weakness and, in some cases, muscle pain. Limb pain, particularly leg or foot pain, can also be due to stress fractures, as discussed below. Symptoms of neuropathy, including absent reflexes, may also be present.² Elevated CK levels are rare, but rhabdo­myolysis can occur if hypophosphatemia is present and not treated prior to refeeding. Electromyography may show myopathy and/or neuropathy. Unlike dermatomyositis and polymyositis, muscle edema on MRI is absent. Muscle biopsies of patients with profound weight loss due to anorexia nervosa characteristically demonstrate selective atrophy of type II (i.e., fast twitch) muscle fibers without inflammatory infiltrates.^2,3

Osteopenia, osteoporosis and abnormalities of hip architecture can occur in both male and female patients with anorexia nervosa, usually correlating with amenorrhea in female patients and profoundly low testosterone in male patients.⁴ Other hormonal axes, such as growth hormone, adipokine and insulin pathways, may also cause low bone density in patients with anorexia nervosa. Stress fractures, especially of the lower limbs, can occur. The risk of stress fractures is increased not only by low bone density but likely also by serous atrophy, which is thought to provide less mechanical support to the surrounding bone during impact compared to normal cellular bone marrow.¹

Treatment

Treatment of anorexia nervosa includes psychiatric treatment and refeeding, which reverses serous atrophy and many of the other changes discussed above. Unfortunately, bone density rarely returns to normal.⁴

Anna Helena Jonsson, MD, PhD, is a senior rheumatology fellow at Brigham and Women’s Hospital in Boston.

Julia F. Charles, MD, PhD, is an assistant professor in orthopedics and rheumatology at Brigham and Women’s Hospital.

References

1. Boutin RD, White LM, Laor T, et al. MRI findings of serous atrophy of bone marrow and associated complications. Eur Radiol. 2015;25(9):2771–2778.
2. McLoughlin DM, Wassif WS, Morton J, et al. Metabolic abnormalities associated with skeletal myopathy in severe anorexia nervosa. Nutrition. 2000;16(3):192–196.
3. McLoughlin DM, Spargo E, Wassif WS, et al. Structural and functional changes in skeletal muscle in anorexia nervosa. Acta Neuropathol. 1998;95(6):632–640.
4. Misra M, Klibanski A. Anorexia nervosa and bone. J Endocrinol. 2014;221(3):R163–R176.