Teaching Case

A 66-year-old man with no past medical follow-up for decades came to our emergency department complaining of worsening fatigue, dyspnea, orthopnea and paroxysmal nocturnal dyspnea. He referred to having these symptoms for years and that they became unbearable over the last couple of days. Blood scan showed normal leucocytes and elevated C-reactive protein.

A thoracoabdominal angioscan was performed to look for a cause for these symptoms. It showed extensive circumferential soft tissue sheathing of the thoracic and abdominal aorta (“coated aorta"), as well as its branches. The aortic arch was also involved. A bilateral pleural effusion was also noted.

We could also see bilateral symmetric peri-nephric fat stranding ("hairy kidney").

The inferior vena cava is spared.

Erdheim–Chester disease and lymphoma were the suggested differential diagnoses at this point.

A biopsy of the periaortic tissue was performed in order to confirm the diagnosis.

Erdheim–Chester disease (ECD) is a rare form of non-Langerhans' cell histiocytosis, originally described in 1930 as "Lipid Granulomatosis" [1]. It is a systemic disorder characterized by diffuse histiocytic infiltration of the bones and various organs [1].

It primarily affects adults between their 5th and 7th decades of life, with a slight male predominance [1]. Patients with ECD have a variable clinical course, ranging from an indolent focal disease to life-threatening organ failure [2].

Histologically, it is characterized by the presence of lipid-laden histiocytes with foamy or eosinophilic cytoplasm, which are positive for CD68 and negative for CD1a [3].

Bone pain represents the most common symptom and usually involves the lower limbs [2]. Other common presenting symptoms include non-specific complaints such as fever, weakness, weight loss, night sweats and fatigue [1].

Imaging plays a key role in diagnosing ECD. The most frequent organ affected are the bones, with bilateral symmetric osteosclerosis of the metadiaphysis of the femur, tibia, and fibula considered pathognomonic [1]. Other common radiological manifestations include periaortic soft tissue encasement, pericardial and pleural effusions, myocardial and CNS infiltration, interstitial lung disease and infiltrative perinephric soft tissue thickening (“hairy kidney") [4].

The rarity of ECD coupled with multi-organ involvement can make the diagnosis extremely challenging and often requires integration of descriptive pathology together with clinical and radiographic findings [4]. Tissue biopsy is required in all ECD cases, not only to confirm the diagnosis, but also to identify associated mutations for therapeutic purposes [4].

Various therapies for ECD have been reported. FN-α-based regimens have been shown to improve survival and have been widely used in the therapy of ECD [5]. However, the most promising advances in this disease´s treatment have been the demonstration of efficacy for BRAF inhibitors and MEK inhibitors [5], as these medications are now recommended as 1st line options depending on mutational testing [4].

All patient data have been completely anonymised throughout the entire manuscript and related files.