Nonspecific Focal Myositis as a Rare Complication of Anorexia Nervosa in an Adolescent Girl

Sir, We report the case of a 13-year-old girl with a background of obsessive-compulsive disorder and anorexia nervosa who presented with progressive difficulty in walking for 3 months and inability to extend both knees for the past 2 weeks. The pain was localized to the posterior aspect of both knees, associated with low-grade fever. There was no back pain, radiculopathy, upper limb involvement, bowel or bladder complaints, sensory disturbances, or systemic features suggestive of connective tissue disease. She had a history of decreased food intake due to fear of weight gain, compulsive handwashing, and behavioral problems for 1 year. On examination, she was malnourished, underweight, and pale. Vital signs were stable. Oral examination revealed whitish lacy lesions consistent with lichen planus. Neurological examination was normal. Musculoskeletal examination showed tenderness in both popliteal fossae. Other systems were unremarkable. Investigations revealed hemoglobin: 12.3 g/dL, erythrocyte sedimentation rate: 31 mm/h, C-reactive protein: 1.4 mg/L, normal renal, liver, thyroid, and coagulation profiles. Autoimmune workup, including antinuclear antibody (ANA), ANA profile, antiphospholipid antibodies, anti-thyroid peroxidase antibody, and rheumatoid arthritis factor, was negative. Serum Creatininephosphokinase (CPK) and electromyography were normal. Magnetic resonance imaging revealed inflammatory changes in the posterior compartment muscles of the proximal legs, suggestive of myositis [Figure 1]. Muscle biopsy showed muscle fiber size variation with both hypertrophic and rounded-angular atrophic fibers, suggesting focal myositis.Figure 1: Magnetic resonance imaging revealed inflammatory changes in the posterior compartment muscles, suggestive of myositisShe was managed with nutritional supplementation, psychotherapy, behavior therapy, and physiotherapy. She demonstrated marked improvement at 1-month follow-up. Skeletal muscle involvement in anorexia nervosa is rare. McLoughlin et al. demonstrated histologically confirmed myopathy in severely malnourished patients, often with proximal muscle weakness, diminished lactate response to ischemic exercise, reduced serum carnosinase activity, and normal or only mildly elevated creatine kinase levels.[1] Other reports have described metabolic myopathy, focal weakness, or even pseudo-myasthenic presentations in anorexia nervosa, all of which improved with nutritional rehabilitation.[2-4] Our case adds to this spectrum by highlighting a pediatric patient with nonspecific myositis, normal CPK, and fixed flexion deformity, with complete recovery on nutritional and psychiatric support. Awareness of this rare complication is essential to avoid misdiagnosis as autoimmune connective tissue disease and to ensure timely multidisciplinary management. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.