A recent study published in Clinical Case Reports describes a 50-year-old man diagnosed with systemic mastocytosis with an associated hematologic neoplasm (SM-AHN) even though he had few of SM’s typical symptoms.
The report highlights the complexity of diagnosing SM, as it can mimic other diseases when traditional signs such as skin involvement are missing.
The patient presented with weakness, fatigue, body aches and a swollen abdomen. He did not have a history of hives, rashes or other skin lesions that often raise suspicion for SM. Moreover, he had no family history of autoimmune or systemic diseases. Physical examination confirmed the absence of skin involvement but showed hepatosplenomegaly, or an enlarged liver and spleen. Blood testing revealed elevated white blood cell counts and anemia.
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A bone marrow biopsyBone marrow biopsy A procedure to collect a sample of bone marrow using a needle. Often used to examine the characteristics of mast cells and diagnose SM. showed that the marrow contained a much greater percentage of blood-forming cells than expected. Initially, the care team determined that these findings were consistent with a diagnosis of chronic myeloid leukemia. However, upon reviewing the biopsy findings again, they identified clusters of abnormal mast cells.
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Genetic testing later ruled out chronic myeloid leukemia, along with other myeloproliferative neoplasms (MPNs). It did uncover the KIT D816V mutation, though. Together with the patient’s other clinical and immunohistochemical findings, the investigators diagnosed SM-AHN.
What is a KIT gene mutationKIT gene mutation Most SM cases are caused by the KIT D816V mutation. The KIT gene codes for a type of protein called a receptor tyrosine kinase, which signals mast cells to grow, divide and move.?
SM is usually caused by a sporadic mutation in the KIT gene, which codes for a protein called CD117 transmembrane tyrosine kinase. The protein is involved in the growth, survival and migration of mast cells. The most common KIT mutation associated with SM is the D816V mutation, which results in the amino acid aspartic acid being replaced by the amino acid valine in the protein chain.
Upon diagnosis, the patient began treatment with cladribine, a chemotherapy drug that destroys abnormal white blood cells, for eight days. He experienced no side effects other than mild heartburn, which was successfully treated with omeprazole. He was discharged from the hospital on a regimen of 300 mg hydroxyurea twice per day.
After eight weeks, the individual reported significant improvements in weakness and fatigue, with notably reduced abdominal swelling. Blood testing showed improvements in white blood cell counts, though they still remained elevated.
When comparing this case to previous case reports, the authors noticed a pattern: “SM presenting without skin lesions tends to occur in older adults, carries a greater burden of visceral organ involvement, and is frequently diagnosed with delay due to the absence of the classic cutaneous prompt,” they noted.
