Teaching NeuroImages: Ataxia and diabetes insipidus

Neurohistiocytosis of the Cerebellum: A Rare Cause of Ataxia

Erdheim-Chester disease (ECD) is a non-Langerhans cell histiocytosis that affects multiple body organs, notably the skeletal system. We examined a 58-year-old man who presented with ataxia and T2 hyperintensity of the middle cerebellar peduncles and dentate nuclei without contrast enhancement on MRI brain. Workup for malignancy revealed "hairy kidneys" on CT scan of the abdomen, and excisional biopsy of the retroperitoneal mass for concerns of lymphoma revealed foamy histiocytes that tested positive for CD68 and negative for CD1a, confirming the diagnosis of ECD. Further genetic testing on excised tissue revealed BRAF (V600E) gene mutation that is present in 50% of ECD patients. Treatment was initiated with targeted therapy using the BRAF inhibitor Dabrafenib. X-ray of the lower extremities did not reveal sclerosis of the long bones, and bone scan with technetium 99 was negative except for a nonspecific tracer uptake in left calvarial bone with no corresponding CT changes or T1/T2 signal changes on MRI. His MRI brain revealed classic cerebellar involvement in ECD without other central nervous system (CNS) involvement. It has been postulated that bone involvement is almost universal in ECD; however, our patient with ECD had ataxia and cerebellar involvement without significant bone involvement, as evidenced by bone scan. This is a rare presentation of ECD affecting the CNS and sparing the skeletal system. It confirms the wide spectrum of presentation this multisystem disease can have.

The role of 18FDG, 18FDOPA PET/CT and 99mTc bone scintigraphy imaging in Erdheim-Chester disease

Erdheim-Chester disease (ECD) is a rare non-Langerhans cell histiocitosis, characterized by multisystemic xanthogranulomatous infiltration by foamy histiocytes that stain positively for CD68 marker but not express CD1a and S100 proteins. Etiology and pathogenesis are still unknown and only about 500 cases are related in the literature. Multisystemic involvement leads to a wide variety of clinical manifestations that results in a poor prognosis although recent advances in treatment. We present the clinical, nuclear medicine findings and therapeutic aspects of a serie of 6 patients with histopathological diagnosis of ECD, who have undergone both bone scintigraphy (BS) and 18F-fluorodeoxyglucose (18FDG)-PET/CT scans in our institution. A complementary 18F-fluorodopa (18FDOPA)-PET/CT was performed in one case. Three different presentations of the disease were observed in our casuistic: most indolent form was a cutaneous confined disease, presented in only one patient. Multifocal involvement with central nervous system (CNS) preservation was observed in two patients. Most aggressive form consisted in a systemic involvement with CNS infiltration, presented in three patients. In our experience neurological involvement, among one case with isolate pituitary infiltration, was associated with mortality in all cases. 18FDG-PET/CT and BS were particularly useful in despite systemic involvement; locate the site for biopsy and the treatment response evaluation. By our knowledge, 18FDOPA-PET/CT not seems useful in the initial staging of ECD. A baseline 18FDG-PET/CT and BS may help in monitoring the disease and could be considered when patients were incidentally diagnosed and periodically 18FDG-PET/CT must be performed in the follow up to evaluate treatment response.

Complete remission of critical neurohistiocytosis by vemurafenib

Objective:

To describe a patient with life-threatening brainstem neurohistiocytosis who recovered completely upon targeted treatment with the V600E mutation-specific BRAF inhibitor vemurafenib.

Methods:

We report clinical, histiologic, genetic, and sequential imaging findings, including fluorodeoxyglucose (FDG)-PET, over a follow-up period of 11 months.

Results:

The patient presented with central hyperventilation, skeletal and perirenal Erdheim-Chester disease, and cutaneous Langerhans cell histiocytosis. A BRAF V600E hotspot mutation was detected in all afflicted tissues. Therapy with vemurafenib led to complete and stable clinical remission of CNS lesions and systemic disease that could be demonstrated by brain MRI and whole-body FDG-PET.

Conclusions:

Neurologic involvement in Erdheim-Chester disease usually confers a poor prognosis. In this patient, vemurafenib was well-tolerated and highly efficacious for severe brainstem involvement in Erdheim-Chester disease with overlapping Langerhans cell histiocytosis. This case illustrates the heterogeneous phenotypic spectrum of neurohistiocytosis and underscores the importance of genetic testing.

Classification of evidence:

This article provides Class IV evidence. This is a single observational study without controls.