Intense Fluorodeoxyglucose Uptake in Aggressive Systemic Mastocytosis without Associated Hematological Neoplasm

Unusual Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography Presentation

Abstract

Systemic mastocytosis (SM) is a relatively rare heterogeneous group of disorders characterized by uncontrolled proliferation and accumulation of clonal mast cells in one or more organs. Indolent SM is the most common variety. Less common variety is aggressive systemic mastocytosis (aSM) type with or without associated hematological neopalsm (AHN). Fludeoxyglucose (FDG) positron emission tomography/computed tomography has a limited role in aSM without AHN as these exhibit low FDG avidity. We are presenting a biopsy-proven case of aSM without AHN showing abnormally high FDG uptake in lesions involving skin, nodes, marrow, and muscles.

Introduction

Mastocytosis is a heterogeneous group of disorders characterized by uncontrolled proliferation and accumulation of clonal mast cells in one or more organs.[¹] Molecular hallmark is c-kit D816V mutation, and in <20% of cases, either a different mutation or no mutation has been reported.[²] The most common presentation is a cutaneous lesion (urticarial pigmentosa) without organ dysfunction and anaphylaxis caused by the release of mast cell mediators (80% – Indolent systemic mastocytosis [ISM]). In 15% of cases, it follows an advanced course such as aggressive SM (aSM), SM with associated hematological neoplasm (AHN), MC leukemia, or sarcoma with dysfunction of one or more organs.[²] The low prevalence and unusual features of SM often hinder its diagnosis for several years.[³] Fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) imaging is considered not a sensitive tool for mast cell activation and proliferation which cannot distinguish between indolent and purely aSM.[²]

We are presenting a case of a young man with biopsy-proven aSM without AHN disease showing abnormally high metabolic activity on FDG PET/CT imaging which is atypical and unusual for the condition.

Case Report

A 37-year-old male presented with a 3-month history of maculopapular cutaneous lesions (urticaria pigmentosa) over the neck and both upper arms, recurrent low-grade fever, and episodes of bronchospasms. Contrast-enhanced computerized tomography performed revealed lymphadenopathy in the bilateral neck and mediastinum, with splenomegaly and areas of skin thickenings in the neck and both upper arms. His skin biopsy (December 28, 2021) revealed mastocytosis, and bone trephine from the sternum (January 12, 2022) revealed bone marrow involvement by mastocytosis with normal erythroid and myeloid precursors. Histopathological diagnosis was aSM without AHN. To evaluate the extent of disease and response evaluation to therapy, an FDG PET/CT was performed. Noncontrast low-dose FDG PET/CT was performed using Celestion, Cannon (Japan).

FDG PET/CT revealed hypermetabolic enlarged lymph nodes in bilateral neck (largest in left supraclavicular (47 mm × 36 mm SUVmax 10), axillae (right 22 mm × 34 mm SUVmax 11.4), and mediastinum (largest right paratracheal 44 mm × 30 mm SUVmax 10) [Figure 1a-i]. The spleen was enlarged (170 mm CC) with diffuse FDG uptake (SUVmax 5.8). Mild diffuse marrow uptake with small focal deposits was seen to suggest marrow disease. There were also multiple hypermetabolic deposits in muscles of the neck, shoulders, and both pectoral regions and hypermetabolic skin lesions over the right anterolateral chest wall and sternal (SUVmax 10.5) regions [Figure 1a-i].

Figure 1: (a-i) FDG PET/CT (without intravenous contrast) scan (a) MIP image showing areas of hypermetabolism in the neck, chest, splenomegaly, and enhanced marrow uptake (b and c) Axial images showing intense FDG uptake in nodes and muscles (d and e) hypermetabolic skin thickening anterior to manubrium sterni (f and g) enlarged spleen with diffusely increased FDG uptake (h and i) Focal marrow uptake of FDG in right sacral ala. FDG PET/CT: Fludeoxyglucose positron emission tomography/computed tomography presentation, MIP: Maximum intensity projection

Discussion

SM is a relatively rare disease with a reported prevalence of 1 in 10,000 persons.[^4,5] According to a multicenter French study, FDG PET/CT imaging shows no significant metabolic activity in smoldering and purely aSM without AHN but intense FDG uptake in the marrow and other sites seen in aSM with AHN.[²] In a recently published case report by Koukalová etal., a patient with aSM had diffusely low FDG uptake on lesions seen on CT but enhanced marrow uptake and marrow biopsy revealed kit D816V mutation, which is considered minor criteria for diagnosing SM.[⁶] In contrary to above mentioned case, our case revealed intense FDG uptake overall. Based on these published facts, FDG PET/CT is considered to have limited utility for estimating the prognosis and assessing the therapeutic effects in ISM and aSM without AHN. Interestingly, our patient with aSM without AHN revealed intense hypermetabolism. It is also important to mention that our case also exhibited significant mast cell infiltration in various muscle groups, which is an unusual finding. This case report also favors the utility of FDG PET/CT in response evaluation in such rare with positive baseline FDG PET/CT (although we do not have a posttreatment FDG PET/CT). We conclude that this case report would add to existing data showing an unusual presentation of aSM without AHN showing intense FDG uptake which is considered to have low-to-no FDG avidity. In these patients, FDG PET/CT may be used for response assessment.

Informed consent

Written informed consent was obtained from the patient for publication.

Declaration of patient consent

The authors certify that they have obtained appropriate patient consent for conducting tests and using clinical information for publication as per institutional policy. The patient understands that his name and initials will not be published and due efforts will be made to conceal his identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.