Case Report

Systemic Mastocytosis: A Mimicker of Reactive Arthritis

Table 1

Bone marrow biopsy results and laboratory data.

TestResult

Bone marrow biopsy results
Flow cytometryNo evidence of acute leukemia or increased blasts
CD25Positive
CD68Weakly positive
CD117Positive
CD3, CD5, CD10, CD20, CD34, MPO, TDT, cyclin D1, DBA-4A, BCL6Negative
Ki675%
Full-leukemia panel for translocationNegative
Karyotype46 XX
Histology90% cellular bone marrow
Diffuse population of medium-sized cells with round to kidney-shaped nuclei, and moderate to abundant cytoplasm with retraction, seen surrounding aggregates of small lymphocytes and admixed with increased eosinophils

Blood test done while on midostaurin 2 weeks prior to presentation:
CBCHb: 10.3 g/dL
MCV: 103.7 fL
WBCs: 4100/µL
Neutrophils: 70%
Lymphocytes: 21%
Eosinophils: 4%
Platelets: 117000/µL

Blood test in the ED on presentation
CBCHb: 7.8 g/dL
MCV: 104.2 fL
WBCs: 3500/µL
Neutrophils: 74%
Lymphocytes: 15%
Eosinophils: 3%
Platelets: 75000/µL
CRP172 mg/dL
ESR119 mm/h
Procalcitonin0.45 ng/mL

Urine studies in the ED on presentation
Urine analysisWBCs: numerous; RBCs: 2–4
Leukocyte esterase: negative; nitrites: negative; squamous epithelia: present casts: negative; crystals: negative; bacteria: negative
Urine cultureNegative

Infectious workup during admission
PCR (parvovirus, adenovirus, chlamydia, gonorrhea, TB)Not detected
Bacterial cultureNegative
Fungal cultureNegative
AFB smearNegative
16S RNANegative
Synovial fluid analysisRBCs: 5610/µL; WBCs: 1230/µL; N: 77%; L: 12%; Mono: 8%; Eo: 3%
Synovial fluid polarizing microscopyNo crystals seen
Many RBCs and 10–15 WBCs

ED: emergency department; CBC: complete blood count; CRP: C-reactive protein; ESR: erythrocyte sedimentation rate; WBCs: white blood cells; RBCs: red blood cells; PCR: polymerase chain reaction; TB: tuberculosis; AFB: acid fast bacilli. N: neutrophils; L: lymphocytes; Mono: monocytes; Eo: eosinophils.