Teaching Case

We present a 17-year-old girl with bilateral knee pain with a history of patellar chondropathy. She had recently presented anorexia nervosa with a weight loss of 19 kg in 3 years, and secondary amenorrhoea since 9 months. BMI was 16.3 kg/m2. Physical examination was normal. Laboratory studies revealed leukopenia.

MRI and lower limb radiography performed 18 months before admission were normal.
The new MRI of both knees showed signal abnormalities of both distal femurs leading to the complete MR investigation of the thighs which revealed diffuse, bilateral and symetrical hypointensity of the femoral bone marrow on T1 (Fig 1) with hyperintensity on T2 and STIR images (Fig 2). Distally in both femurs there were some areas of hyperintensity on T1 and hypointensity on T2 sequences. There were no soft tissue, meniscal or ligamental abnormalities.

These findings were consistent with the gelatinous transformation of bone marrow in a setting of severe weight loss.
Gelatinous transformation of the bone marrow (GMT) was first identified by Paul Michael in 1930 [1] during the autopsy of patients with prolonged starvation, hence the term “starvation marrow“.
It is a rare clinico-pathologic condition caracterised by a depletion of fat cells secondary to an important catabolism, associated with interstitial infiltration by a gelatinous substance mainly composed of hyaluronic acid which creates an adverse environment for haematopoietic cells. It results in cytopenia, the degree of which does not necessarily reflect the severity of the bone marrow damage [2].
Histopathological changes of the bone marrow (hypoplastic/aplastic, partial or complete gelatinous degeneration) seem to be correlated with the amount of weight loss, but not to other clinical findings such as age, duration of the disease, and clinical type of anorexia nervosa [3]. Studies have also shown that less severe weight loss can lead to paradoxical increase in marrow fat [4]. Therefore, GMT is mainly seen in patients suffering from severe nutritional deprivation such as in anorexia nervosa, alcoholism, and malabsorption [5] and is usually an incidental finding.
GMT can either have diffuse or focal forms [6] starting in the peripheral skeleton and eventually reaching the axial skeleton, with a progression pattern of the normal bone marrow conversion from haematopoietic to cellular, as seen during childhood [7]. GMT will be recognised on MRI as a fat-poor marrow with a serous-like MRI pattern on all pulse sequences, e.g., low signal on T1 and high signal on T2 and STIR sequences. It can be associated with insufficiency fractures, which may be hidden on MRI by the abnormal bone marrow signal.
The same MRI pattern can be encountered with other pathological processes such as bone marrow infiltrative/proliferative disorders among which the most frequent in children is leukaemia, and also bone marrow replacement disorders such as lymphoma. The diagnosis is based on physical exams and blood tests [8]. Another benign differential diagnosis is the reconversion of the bone marrow which follows a reverse pattern to that seen with marrow conversion in childhood [9], and is a physiological response to increased haematopoietic needs of the body such as in haemoglobinopathy or respiratory disorders.
Bone marrow generally recovers from GMT when the underlying cause is treated especially with adequate nutritional therapy.