Management of Poorly Controlled Indolent Systemic Mastocytosis Using Narrowband UVB Phototherapy

Comment

Systemic mastocytosis is a heterogeneous disorder characterized by the proliferation and accumulation of atypical MCs in tissues, principally in the bone marrow and skin, though involvement of the gastrointestinal tract, liver, spleen, and lymphatic system also have been reported.^1,2,6 The WHO classification of mastocytosis divides this condition into 7 subtypes.⁴ Indolent systemic mastocytosis is the most common variant.^2,6 The etiology of ISM is not fully understood, but there is evidence suggesting that an activating mutation of KIT proto-oncogene receptor tyrosine kinase, KIT (usually D816V), present in the MCs of nearly 80% of patients with ISM may be involved.^1,3-5,7 Patients occasionally present with predominantly cutaneous findings but typically seek medical attention due to the recurrent systemic symptoms of the disease (eg, pruritus, flushing, syncope, palpitations, headache, dyspepsia, vomiting, diarrhea), which are related to the release of MC mediators.^1,2

The management of ISM is complex and based primarily on symptom reduction without alteration of disease course.^1,2,5,7 Patients should avoid symptom triggers such as heat, humidity, emotional and physical stress, alcohol, and certain medications (ie, aspirin, opioids, radiocontrast agents).⁷ Patients are initially treated with histamine H1- and H2-receptor antagonists to alleviate MC mediator release symptoms.^1,2,8 Although H1 blockers are most effective in mitigating cutaneous symptoms and limiting pruritus, H2 blockers are used to control gastric hypersecretion and dyspepsia.² Proton pump inhibitors are useful in patients with peptic ulcer disease who are unresponsive to H2-receptor antagonist therapy.^2,7 Cromolyn sodium and ketotifen fumarate are MC stabilizers that help prevent degranulation, which is helpful in relieving most major ISM symptoms. Leukotriene antagonists, such as zafirlukast, montelukast sodium, or zileuton, also may be employed to target the proinflammatory and pruritogenic leukotrienes, also products of the MC protein.^2,7 Imatinib mesylate and masitinib mesylate, both tyrosine kinase inhibitors, have been shown to improve symptoms and reduce MC mediator levels in ISM; however, most patients harbor the resistant KIT D816V mutation, which limits the utility of this medication.Patients with sensitive KIT mutations or those who have the wild-type KIT D816 mutation may be more appropriate candidates for imatinib or masitinib therapy, which can ameliorate symptoms of flushing, pruritus, and depression.^7-10 Treatment with omalizumab, a humanized murine anti-IgE monoclonal antibody, can be effective in treating recurrent, treatment-refractory anaphylaxis in ISM patients.^5,7

Symptoms unresponsive to these therapies can be effectively treated with a short course of oral corticosteroids,^6,7 while MC cytoreductive therapies such as interferon alfa or 2-chlorodeoxyadenosine (cladribine/2-CdA) are reserved for refractory cases.^2,7 Alternative therapies such as NB-UVB² or psoralen plus UVA phototherapy¹¹ also have demonstrated success in treating ISM symptoms. In the past, NB-UVB has shown efficacy in controlling pruriginous conditions ranging from chronic urticaria^12,13 to atopic dermatitis¹⁴ to psoriasis.¹⁵ This evidence has spurred studies to evaluate if NB-UVB has a role in the management of uncontrolled cases of cutaneous and ISM.^2,13,16,17 To date, the evidence has been promising. The majority of patients treated with this regimen report subjective reduction in pruritus in addition to clinical cutaneous disease burden.^2,11 Also, laboratory analysis demonstrates decreased levels of tryptase in patients utilizing NB-UVB phototherapy.² Thus far, the use of NB-UVB phototherapy in the treatment of pruriginous disorders such as ISM has not been associated with any severe side effects such as increased rates of anaphylaxis, though some research has suggested that this therapy may lower the threshold for patients to develop symptomatic dermographism.¹² Overall, patients treated with NB-UVB phototherapy report improved quality of life related to more effective symptom control.¹⁶

Although ISM is currently considered an incurable chronic condition,⁶ this case illustrates that symptomatic management is possible, even in cases of long-standing, severe disease. Patients should still be encouraged to avoid triggering factors and be vigilant in preventing potential anaphylaxis. However, NB-UVB phototherapy provides a supplemental or alternative treatment choice when other therapies have failed. We hope that the success of NB-UVB demonstrated in this case provides further evidence that this light-based therapy is a valuable treatment option in mastocytosis patients with unremitting or poorly controlled symptoms.