Introduction Anorexia nervosa (AN) is a psychiatric eating disorder with a prevalence of 0,5%–1% among adolescents, characterised by a decrease in caloric intake, weight loss and behavioural changes. Patients with AN may also suffer from bone marrow suppression and multiple metabolic complications caused by severe malnutrition.

There are 3 main causes of hyperhomocysteinemia: genetic defects, nutritional deficiencies (vitamins B12, B6 or folate) and insufficient elimination. The homocysteine plasma level in patients with AN is linked to cognitive impairment and depression, the latter being the most common psychiatric comorbidity.

Case-presentation We describe the case of AN in a 15 year old female, complicated by extended deep and superficial vein thrombosis of the upper limb. She also had a mild form of depression. At the admission, she presented flat affect, a BMI of 13 kg/m², dry skin with trophic changes, loss of muscle mass, resting bradycardia and hypotension. Blood tests indicated hypoglicemia, mild neutropenia and thrombocytopenia, normal liver and renal function, normal serum ionogram.

On the 10^th day of hospitalisation she presented signs of acute inflammation at the left upper limb, at the venous catheter placement. Doppler ultrasonography confirmed findings of the axillary, brachial and cephalic veins consistent with extended new and old thrombi at the left upper limb. Within thrombophilia evaluation, we found a heterozygous MTHFR A1298C mutation, which causes mild hyperhomocysteinemia.

Anticoagulation therapy with subcutaneous Enoxaparin, antidepressant treatment, controlled caloric and vitamin intake, parenteral electrolyte supplementation and bed rest led to the reduction of the thrombi and the improvement of the biological and clinical condition of the patient.

Conclusions Hospitalised patients with AN can have a complex coagulation profile, with elements of hypocoagulopathy (thrombocytopenia and elevated INR) and of hypercoagulability, like immobilisation and hyperhomocysteinemia. The latter, which is a hallmark for AN, is linked to a high risk of cardiovascular disease, stroke and peripheral vascular disease. There is a study in which thromboelastography was used to evaluate the coagulation status of patients with severe AN and assist in guiding venous thrombosis prophylaxis therapy. Among the psychiatric disorders, AN is associated with the highest mortality rate, with numerous complications, requiring a multidisciplinary approach.