A case report exploring the diagnosis of a woman with indolent systemic mastocytosis (SM) despite the absence of classic symptoms was recently presented in a poster at the North Texas Research Forum 2025.
The 61-year-old woman presented with an itchy rash that was visible over her trunk and limbs. These rashes have been present for the last 43 years. In her teenage years she had been diagnosed with urticaria pigmentosaUrticaria pigmentosa A skin condition marked by itchy, red-to-brown spots, especially on the neck, limbs and torso. It is caused by surplus mast cells and occurs in up to 85% of patients with SM., a skin condition in which spots that cause considerable itching may appear. In addition to the itching, the patient also described experiencing episodes of brain fog since her teen years.
The itching (pruritus) has grown considerably worse to the point that she was unable to carry out activities of daily living. The itching was described as being “unbearable” when she performed certain activities, such as exercising or bathing with warm water.
A physical examination confirmed the presence of reddish-brown macules and patches on the patient’s trunk and upper and lower limbs. These patches were more concentrated on the patient’s lower legs. When these patches were stroked firmly, wheals were formed, which indicated a positive Darier’s sign. A positive Darier’s sign is commonly observed in patients with SM.
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A biopsy of the skin showed an abnormal increase in mast cellMast cell A type of white blood cell produced in the bone marrow. They help defend against infections and play a key role in allergic reactions. In SM, mast cells become overactive and build up throughout the body. concentration. Laboratory investigations revealed elevated serum tryptaseTryptase A protein enzyme that is primarily produced by mast cells and stored in small pockets within the cells, known as granules. High levels of tryptase are a key indicator of SM. (68 ng/mL). 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 multifocal dense infiltration of mast cells. However, genetic testing was negative for the KIT D816V mutation, which is commonly associated with SM. The patient had also never experienced many of the classic symptoms of SM, such as anaphylaxisAnaphylaxis A severe allergic reaction that can turn fatal without treatment. Patients with SM are at a higher risk of developing anaphylaxis. and bone pain.
Nevertheless, the patient’s condition met the clinical criteria for indolent SMIndolent SM A subtype of nonadvanced SM caused by the abnormal accumulation of mast cells in the bone marrow and other organs. Indolent SM accounts for around 90% of SM cases.. Since diagnosis she has received various treatments, including montelukast, omalizumab, cetirizine, and topical clobetasol. She continues to report experiencing flares despite these therapies.
“[Indolent SM] can present atypically, as seen in this patient who lacked systemic symptoms despite multifocal mast cell infiltrates, emphasizing the variability in clinical presentation,” the report’s authors wrote.
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