The spectrum of mastocytosis

Anetodermic mastocytosis: response to PUVA therapy

Mastocytosis is a group of disorders characterized by the accumulation of mast cells in different tissues and organs. The skin is the most frequently involved organ (90% of cases) where mastocytosis may show a heterogenic clinical expression. Anetodermic lesions are an unusual clinical presentation of mastocytosis. We report a case of anetodermic mastocytosis in a 26-year-old man, with sparse lesions and a benign course. PUVA therapy obtained excellent results in this case. Darier's sign should be investigated in patients with anetodermic lesions of unclear origin in order to exclude cutaneous mastocytosis.

Case report: pathologic long bone fracture in a patient with systemic mastocytosis

Systemic mastocytosis is characterized by clonal proliferation of mast cells, which cause disease by accumulating in various organs and releasing their chemical products into tissues. We highlight a patient with systemic mastocytosis that caused a pathologic femur fracture in a 63-year-old man with minimal trauma. The typical presentation of bone involvement is a combination of mixed sclerotic and osteolytic lesions, but this patient also had osteopenia. Although bone involvement is common in patients with systemic mastocytosis, pathologic fractures outside the vertebral column are rare. The patient was treated with intramedullary fixation of his femur and retained adequate fixation at the time of his death 7 months postoperatively. We review the literature on pathologic fractures outside the vertebral column in patients with systemic mastocytosis.

Systemic Mastocytosis: Clinical Manifestations and Differential Diagnosis

Mast cells produce symptoms by local and remote effects of mediator release and by their presence in increased numbers in normal tissue and bone marrow, where they damage and impair normal organ function. Moreover, mast cells are long-lived and heterogeneous in their response to secretagogues and to inhibitors of mediator release. Clinicians sorting out the diagnosis of SM on the basis of presenting signs and symptoms continue to have their diagnostic skills challenged because of the rarity of this disorder, the fact that many symptoms of SM are present in more common disorders, and the multiple guises that SM may assume at the time of presentation.

Cutaneous mastocytosis in children: a clinical analysis of 71 cases

OBJECTIVE

To characterize the clinical features, response to therapy, evolution and prognosis of cutaneous mastocytosis in children.

BACKGROUND

Mastocytosis in children, instead of being induced by a potentially oncogenic c-kit mutation, is probably a clonal disease with benign prognosis.

METHODS

The clinicopathological features, evolution and response to treatment were analysed in 71 children with mastocytosis.

RESULTS

There were 53 (75%) cases of urticaria pigmentosa, 12 (17%) cases of mastocytoma, and six (8%) cases of diffuse cutaneous mastocytosis. In 92% of cases disease onset was in the first year of life. There was a male predominance 1.8 : 1. Treatment did not modify the disease evolution. Eighty per cent of patients improved or had spontaneous resolution of the disease.

CONCLUSION

The most frequent clinical form of mastocytosis was urticaria pigmentosa followed by mastocytoma and diffuse cutaneous mastocytosis. Darier's sign was present in 94% of cases. A negative Darier's sign does not rule out mastocytosis. In contrast to adults, mastocytosis in children usually has a benign course making sophisticated or invasive diagnostic tests unnecessary. A classification of paediatric cutaneous mastocytosis is proposed.

Treatment of systemic mast cell disorders

The heterogeneous nature of disease manifestations in mastocytosis requires the individualization of therapy to each patient's clinical presentation and prognosis. The mainstay of treatment for most categories of mastocytosis are H1 and H2 antihistamines with the addition of corticosteroids for more severe symptoms. This article presents a summary of treatment strategies for indolent and aggressive forms of mastocytosis along with a discussion of future therapeutic directions.

Response of severe systemic mastocytosis to interferon alpha

Six patients with documented systemic mast cell disease were enrolled in a 1-year, phase I study to determine the possible benefits of interferon alpha-2b (IFN-alpha). IFN-alpha therapy was begun at a dosage of 0.5 million units/day (MU/day) by subcutaneous injection and increased, as tolerated, to 3.0 MU/day. Subsequent dose modifications were made based on clinical tolerance and response. No immediate, adverse reactions to IFN-alpha occurred. Several patients showed symptomatic improvement. In two patients ascites resolved and did not recur. Two other patients reported improved energy levels and had decreased size of retroperitoneal, measenteric and retrocrural nodes. One patient failed to benefit and died shortly after completing 12 months of therapy. Bone marrow mastocytosis decreased by 5% to 10% after 12 months of therapy with IFN-alpha. Although five of the six patients had a decrease in the urinary excretion of 1-methyl-4-imidazole acetic acid, serum tryptase values did not appreciably change in any patient. Side-effects from IFN-alpha included hypothyroidism, thrombocytopenia and depression. It is concluded that although treatment with IFN-alpha was associated with a decline in bone marrow mastocytosis and reduced excretion of histamine metabolites, prolonged therapy may be needed and dose-limiting side-effects are frequent.

Systemic mast cell disease associated with the hypereosinophilic syndrome

Systemic mast cell disease (SMCD) is an uncommon disorder characterized by a proliferation of mast cells involving the bone marrow, spleen, liver, skin, and lymph nodes. Although rare, the association of SMCD and other hematologic disorders is well established. To our knowledge, however, no previously published reports have described SMCD associated with the hypereosinophilic syndrome (HES). Herein we describe two patients who had SMCD in association with HES. Both patients had evidence of cardiac eosinophilic involvement, and both responded to systemic therapy. SMCD is often associated with eosinophilia and may be associated with HES more frequently than is commonly appreciated. Because congestive heart failure is a major cause of morbidity in patients with HES, cardiac assessment in patients with eosinophilia and SMCD is important in order to identify those with eosinophilic organ involvement and treat them aggressively.

Clonal eosinophilic disorders and the hypereosinophilic syndrome

An increase in the blood eosinophil count may occur in a number of disease states including allergies, parasitic infections, vascular disease and as a reaction to the presence of malignant tumours. This article defines those disorders that are not purely reactive, and describes in detail the diagnosis and features of clonal eosinophilic disorders and the hypereosinophilic syndrome. The clonal disorders that are associated with eosinophilia are discussed, in particular the acute and chronic eosinophilic leukaemias and clonal eosinophilias in association with acute myeloid leukaemia, myeloproliferative disorders and myelodysplastic syndromes. Whether eosinophilia is produced by a clonal or reactive disorder, the end result can often be the same, i.e. end organ damage produced by sustained hypereosinophilia in the presence of eosinophil activation. When no cause for the eosinophilia leading to the end organ damage is found, this disease is termed 'idiopathic hypereosinophilic syndrome'. Its pathogenesis, clinical features and management are discussed with particular reference to the possibility of it being a T-cell-associated disorder.

Bullous mastocytosis in an infant associated with the use of a nonprescription cough suppressant

Bullous mastocytosis is an unusual expression of mastocytosis typically seen in young children, and many causes of the acute mast cell degranulation with bulla formation have been identified. We report a 6-month-old boy with urticaria pigmentosa and an extensive bullous eruption associated with the ingestion of a nonprescription cough suppressant containing dextromethorphan. The pathogenesis of mastocytosis and the care of patients with this disease are discussed.

Urticaria pigmentosa and juvenile xanthogranuloma: case report and brief review of the literature

Juvenile xanthogranuloma and urticaria pigmentosa are well described in the dermatologic literature. We recently observed a 9-month-old boy with the two diseases occurring concomitantly. This rare combination is described and a brief review of the literature is given.

Evaluation and outcomes of patients with palpitations

PURPOSE

To determine: (1) the etiologies of palpitations, (2) the usefulness of diagnostic tests in determining the etiologies of palpitations, and (3) the outcomes of patients with palpitations.

PATIENTS AND METHODS

One hundred and ninety consecutive patients presenting with a complaint of palpitations at a university medical center were enrolled in this prospective cohort study. Patients underwent a structured clinical interview and psychiatric screening. The charts were abstracted for results of the physical exam and tests ordered by the primary physician. Assignment of an etiology of palpitations was based on strict adherence to predetermined criteria and achieved by consensus of the two physician investigators. One-year follow-up was obtained in 96% of the patients.

RESULTS

An etiology of palpitations was determined in 84% of the patients. The etiology of palpitations was cardiac in 43%, psychiatric in 31%, miscellaneous in 10%, and unknown in 16%. Forty percent of the etiologies could be determined with the history and physical examination, an electrocardiogram, and/or laboratory data. The 1-year mortality rate was 1.6% (95% confidence interval [CI] 0% to 3.4%) and the 1-year stroke rate was 1.1% (95% CI 0% to 2.6%). Within the first year, 75% of the patients experienced recurrent palpitations. At 1-year follow-up, 89% reported that their health was the same or improved compared to that at enrollment, 19% reported that their work performance was impaired, 12% reported that workdays were missed, and 33% reported accomplishing less than usual work at home.

CONCLUSIONS

The etiology of palpitations can often be diagnosed with a simple initial evaluation. Psychiatric illness accounts for the etiology in nearly one third of all patients. The short-term prognosis of patients with palpitations is excellent with low rates of death and stroke at 1 year, but there is a high rate of recurrence of symptoms and a moderate impact on productivity.

Southwestern Internal Medicine Conference: mastocytosis: developments during the past decade

Mastocytosis is a spectrum of disorders characterized by an aberrant proliferation of tissue mast cells. Although this disease process often affects the skin, it may involve multiple organs. The clinical disorder varies according to patient age, the clinical manifestations demonstrated, and the extent of the mast cell proliferative process. A myriad of clinical symptoms occur, and these may be localized to the organ system involved or may be systemic, depending on whether there is local or generalized mast cell mediator release. Diagnosis includes the demonstration of increased tissue mast cells in involved organs as well as increased levels of biochemical mediators. Patients with cutaneous involvement only have the best prognosis. Treatment is directed toward stabilizing mast cell mediator release and blocking the effects of those mediators generated.

Hematologic manifestations of systemic mast cell disease: a prospective study of laboratory and morphologic features and their relation to prognosis

PURPOSE

Systemic mast cell disease (SMCD) follows an indolent course in most patients, but a significant number of patients die of neoplastic hematologic disorders. Reviews of the literature and retrospective studies in a single institution have defined features that may be associated with a poor prognosis, but prospective studies have been lacking. Therefore, we prospectively analyzed the relationship between clinical, laboratory, and hematopathologic findings and clinical outcome in a series of 46 patients with mast cell disease. This analysis was employed to both define clinically useful prognostic variables and describe the histologic evolution of bone marrow mast cell infiltration and its relationship to hematologic neoplasia.

PATIENTS AND METHODS

Forty-six adult patients were referred to the National Institutes of Health (NIH) with clinical and/or pathologic evidence of mast cell proliferation. All patients had bone marrow examinations, and 10 patients underwent serial bone marrow biopsies. The diagnosis of SMCD required pathologic documentation of bone marrow mast cell infiltrates. The patients were followed for up to 13 years at the NIH (up to 30 years after the initial pathologic diagnosis of mast cell disease). Statistical analysis defined the correlation between variables and the presence of diagnostic bone marrow lesions. The Kaplan-Meier method was used to construct survival curves, and the effects of various variables on the survival time were examined.

RESULTS

Thirty-two of 46 patients (74%) had a bone marrow biopsy diagnostic for SMCD. The remaining 14 patients were considered to have cutaneous mast cell disease (CMCD). Univariate analysis showed that hepatosplenomegaly, alkaline phosphatase level, absolute lymphocyte count, and age at onset of symptoms were positively correlated with SMCD, whereas hemoglobin level was negatively associated with diagnostic bone marrow lesions. With multivariate analysis, only hemoglobin and absolute lymphocyte count remained as significant independent predictors of bone marrow findings. No CMCD patient died or had significant clinical deterioration in the 1- to 30-year period of follow-up (median = 8.5 years), whereas 10 of 32 SMCD patients (31%) died from 1 to 22 years after diagnosis (median = 2.5 years) (p less than 0.0001). Univariate analysis revealed the following variables as significantly increasing the risk of death in patients with SMCD: later onset of symptoms, absence of cutaneous mastocytosis, thrombocytopenia, elevated lactate dehydrogenase (LDH) level, anemia, bone marrow hypercellularity, qualitative peripheral blood smear abnormalities, elevated alkaline phosphatase level, and hepatosplenomegaly. Multivariate analysis showed that only the age at onset of symptoms and LDH levels were significant independent predictors of survival. Eight of the 10 SMCD patients who died had myeloproliferative or myelodysplastic syndromes or acute nonlymphocytic leukemia.

CONCLUSION

Our prospective study has defined a number of important variables in patients with clinical evidence of mast cell proliferation that can predict both the presence of SMCD and the likelihood of fatal disease. Since recent evidence suggests that mast cells derive from a bone marrow hematopoietic progenitor, SMCD may represent a myeloproliferative condition with the propensity to evolve into a neoplastic granulocytic disorder in a significant minority of patients.

An unusual form of chronic myeloproliferative disorder. Aleukemic basophilic leukemia

A 52-year-old Japanese man manifested various clinical signs and symptoms such as vomiting, high fever, dyspnea, cough, sweating, palpitation, eosinophilic leukocytosis and hepatosplenomegaly. These histamine-related clinical manifestations showed a dramatic response to steroid therapy. After 10 months of hospitalization, he suddenly succumbed to candidal septicemia at the end of the third cycle of steroid therapy. Autopsy revealed neoplastic proliferation of immature basophils in various internal organs without involvement of the skin. The neoplastic cells, positive immunohistochemically for leukocyte common antigen, possessed lobulated nuclei and weakly metachromatic cytoplasmic granules, predominantly of the basophil type, which exhibited weak naphthol ASD-chloroacetate esterase activity. Mast cell-type granules were also observed ultrastructurally. The neoplastic infiltration was associated with fibrosis in the liver, spleen and bone marrow and with extramedullary hematopoiesis in the liver, spleen, lymph nodes and perihypophyseal tissue. The bone marrow showed uneven and multifocal involvement. Despite the lack of leukemic manifestations and the results of chromosomal analysis, the most suitable diagnosis was aleukemic basophilic leukemia within the category of chronic myeloproliferative disorder. Kinship of this neoplasia to systemic mastocytosis is discussed.

Malignant mastocytosis with circulating mast cells

A case of malignant mastocytosis with peripheral blood involvement is presented. The course of the patient's illness was complicated by recurrent hypotensive episodes, presumed to have been caused by mast cell degranulation. Treatment with hydroxyurea was associated with persistent hypotension which resulted in death. It has been proposed that the diagnosis of mast cell leukemia be given to patients presenting with greater than 10% atypical mast cells in the blood. However, review of 16 published cases of malignant mastocytosis with circulating mast cells reveals that the clinical manifestations, complications, and survival do not vary significantly with the percentage of peripheral blood mast cells. Patients with malignant mastocytosis with significant involvement by atypical mast cells in the bone marrow and peripheral blood should be considered as having an aggressive disease, regardless of the percentage of circulating mast cells.

A clinical and histological study of urticaria pigmentosa: relationships between mast cell proliferation and the clinical and histological manifestations

In 21 cases of urticaria pigmentosa (UP), clinical and histological observations and evaluation of mast cell (MC) volume density in the lesions using a morphometric point counting method were performed. The mutual correlations between clinical and histological findings were statistically assessed by a method of multiple regression analysis. Clinical items employed in the analyses were as follows: sex, the age of onset, the age of biopsy, the biopsy, the duration of lesions, the type of skin lesions, sites involved, the presence or absence of Darier's sign of Darier's sign and symptoms, and serum histamine level. Histological items included the localization and infiltration pattern of MC, the level of basal melanosis, the presence or absence of inflammatory cell infiltration, and the MC volume density in the lesions. Statistical significance of the partial regression coefficients was obtained for 6 pairs of the criteria (p = 0.05), including the age of onset and the age of biopsy, the age of onset and the level of basal melanosis, the duration of lesions and the level of basal melanosis, and the type of skin lesions and the level of basal melanosis. No significant correlations were observed between the MC volume density in the lesions and any of the other items. These results suggest that the basal melanosis in a UP lesion may not be a direct reaction to the transitory massive infiltration of MC, but rather be due to a relatively long-term effect of MC infiltration. Furthermore, the MC volume density in the lesion is not likely to be an important factor in determining the clinical manifestations of a UP lesion.

Philadelphia chromosome-negative acute hematopoietic malignancy: ultrastructural, cytochemical and immunocytochemical evidence of mast cell and basophil differentiation

We describe a patient with fever and multiple osteolytic bone lesions accompanied by hypercalcemia, a duodenal ulcer, anemia, and thrombocytopenia. Bone marrow showed a dense infiltration by abnormal cells characterized by small basophil granula, erythrophagocytosis and nuclear atypia. These cells were positive for toluidine blue and partly for myeloperoxidase and chloroacetate esterase, expressed myeloid differentiation markers, and exhibited multiple numerical and structural chromosome aberrations. Molecular genetic analysis showed no breakpoint cluster region rearrangement. Electron microscopy demonstrated granula both of basophil and mast cell type. Concluding, in this patient an acute hematopoietic malignancy with many features of malignant mastocytosis but also with signs of a basophil differentiation. This is further support for a hematopoietic stem cell origin of human mast cells.

Shock in an infant with bullous mastocytosis

A 6-month-old infant had bullous lesions on his posterior neck, upper trunk, and extremities for two months prior to admission for fever and shock. He had an elevated white blood cell count with left shift and normal platelet count, but abnormal coagulation studies. He was treated with intravenous antibiotics, crystalloids, fresh-frozen plasma, and pressor agents. A histamine H2 receptor antagonist was started for guaiac-positive nasogastric tube drainage. The patient recovered after four days of treatment. A skin biopsy confirmed mastocytosis. A week later the child passed grossly bloody stools with blood clots. No source of gastrointestinal bleeding was identified by extensive work-up. Blood histamine level measured one day before gastrointestinal bleeding was 16,400 pg/ml (normal 263 +/- 202 pg/ml). The bleeding resolved spontaneously. The patient was maintained on cimetidine. Results of a subsequent bone scan were normal. Shock or gastrointestinal bleeding associated with unusual skin lesions should alert the pediatrician to the possibility of mastocytosis.

Portal hypertension and ascites in systemic mastocytosis

We report a case of systemic mastocytosis (SM) presenting as ascites and portal hypertension. The haematological picture at presentation was suggestive of chronic myelomonocytic leukaemia. Initial difficulties in making a diagnosis of SM were encountered as the cutaneous signs were atypical. The correct diagnosis was established only after tissue sections were appropriately stained for mast cells. The liver biopsy showed portal and sinusoidal mast cell infiltration, portal fibrosis and evidence of hepatic venous outflow obstruction. The disease progressed rapidly and recurrent massive ascites was a dominant problem. This case illustrates again the problems of making a diagnosis of SM especially when the clinical picture is atypical. Ascites as a presenting manifestation of SM has been reported previously in only six patients. Published cases of SM with portal hypertension or ascites or both are reviewed.

Systemic mastocytosis associated with membranous nephropathy and peripheral neuropathy

A report of the occurrence of membranous nephropathy and peripheral neuropathy in a patient with systemic mastocytosis is presented. Previous reviews of patients with systemic mastocytosis have not noted this association. During cyclical therapy with prednisone and chlorambucil in this case, nephrotic-range proteinuria remitted. Peripheral neuropathy resolved 10 months after discontinuation of therapy. Pathophysiological mechanisms resulting in this clinical presentation may be immunologically mediated.

Cutaneous mast cell quantity in pruritic and nonpruritic hemodialysis patients

Pruritus remains a significant complication of end-stage renal disease. Its cause in hemodialysis patients is not known. It has been postulated that increased numbers of mast cells occur in these patients and may account for the presence of pruritus. Our objective was to determine if there is a difference in the number of cutaneous mast cells between pruritic and nonpruritic patients. A 3-mm punch biopsy specimen was obtained from pruritic (n = 7) and nonpruritic (n = 6) hemodialysis patients. We observed no significant difference in the quantity of cutaneous mast cells in pruritic and nonpruritic hemodialysis patients. We conclude that the etiology of pruritus in hemodialysis patients is not related to an increase in the number of cutaneous mast cells.

Ultrastructural morphometric analysis of human mast cells in normal skin and pathological cutaneous lesions

Electron micrographs of human mast cells in normal neonatal and adult skin and in cutaneous lesions of basal cell carcinoma (BCC), hemangioma and mastocytosis were assessed by morphometric analysis. Using this quantitative histologic approach, adult skin mast cells were found to be significantly larger (47.7 microns 2 +/- 2.4 SEM vs. 38.3 microns 2 +/- 1.8 SEM, p less than or equal to 0.001) and have larger granules (0.63 micron +/- .02 SEM vs. 0.53 micron +/- .02 SEM, p less than or equal to 0.001) than infant mast cells while both mast cell populations had comparable nuclear sizes (13.7 microns 2 +/- 0.9 SEM vs. 14.3 microns 2 +/- 0.8 SEM) and numbers of cytoplasmic granules (72 +/- 4.0 SEM vs. 66 +/- 4.0 SEM). Morphometric analysis of mast cell infiltrates in the adult skin lesions of BCC and hemangioma revealed that these cells were larger than neonatal mast cells but were similar to normal adult controls. Cutaneous mast cells from 2 mastocytosis patients, however, had significantly larger mean cell surface areas (78.0 microns 2 +/- 3.4 SEM and 70.6 microns 2 +/- 3.2 SEM, p less than or equal to 0.001), nuclear areas (20.8 microns 2 +/- 1.1 SEM and 21.3 microns 2 +/- 1.2 SEM p less than or equal to 0.001) and granule diameters (0.82 micron +/- 0.4 SEM and 0.83 micron +/- .03 SEM, p less than or equal to 0.001) when compared with mast cells in normal adult skin and in the other pathologic lesions. No difference in the total number of cytoplasmic granules was observed in the different mast cell populations.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro functional reactivities of cutaneous mast cells from patients with mastocytosis

Cutaneous mast cells from 3 patients with mastocytosis were evaluated for their morphologic characteristics and in vitro functional reactivities to different secretory agonists. By electron microscopy, mastocytosis mast cells appeared larger than normal skin mast cells, frequently had atypical, highly indented or bilobed nuclei, and each contained numerous, elongated cytoplasmic projections. Suspensions of mastocytosis mast cells were obtained from lesional skin biopsy specimens, and their response to both immunologic and nonimmunologic secretagogues was compared with mast cells from normal skin. Lesional skin mast cells had a net histamine release of 12.3% (+/- 1.3 SEM) and 31.1% (+/- 6.0 SEM) following stimulation with the purified human anaphylotoxin C3a and mouse monoclonal antihuman IgE antibodies, respectively. This specific release was similar to the responses observed in normal skin mast cells (11.5% +/- 4.5 SEM and 16.7% +/- 2.1 SEM, respectively). Mast cells from cutaneous lesions of mastocytosis also responded to the nonimmunologic secretagogues, morphine sulfate and calcium ionophore A23187 with a specific histamine release of 15.1% (+/- 1.2 SEM) and 39.8% (+/- 8.7 SEM), respectively. The results of this study demonstrate that mast cells from lesions of mastocytosis are morphologically atypical, but have a histamine content similar to normal skin mast cells and retain their functional reactivities to clinically relevant secretory stimuli.

Quantification of cutaneous mast cells using morphometric point counting and a conjugated avidin stain

Mast cells in normal human skin and in lesional cutaneous tissue from two patients with mastocytosis were quantified with the use of a morphometric point counting technic in combination with the mast cell-specific stain, conjugated avidin. Mast cells in normal human flank skin occupied a relatively small percentage of the dermal volume, with a mean value of 0.40% (+/- 0.14 SD), while a marked increase in mast cell content was demonstrated in cutaneous lesional tissue from two patients with the macular and nodular forms of mastocytosis (2.5% and 64.3%, respectively). In a comparative study with the use of morphometric analysis, conjugated avidin proved objectively to be as good as toluidine blue, and subjectively superior to this stain for mast cell identification in both human and murine skin. The combination of morphometric point counting and the conjugated avidin stain provides a useful tool for establishing the diagnosis of mastocytosis and is applicable to a variety of experimental systems.

Unilateral facial telangiectasia macularis eruptiva perstans

A 36-year-old man developed unilateral facial telangiectases over a 10-year period. Histopathologic examination showed collections of mast cells. This patient has an unusual variant of telangiectasia macularis eruptiva perstans. The differential diagnosis of facial telangiectases is discussed. Mastocytosis should be considered in patients presenting solely with telangiectases.

Mastocytosis: a review

Mastocytosis refers to a spectrum of clinical and laboratory abnormalities attributable to tissue infiltration by large numbers of mast cells and to the discharge of various biologically active substances by these cells. It most commonly results in cutaneous manifestations during childhood but may develop at any age or involve almost any organ system. The treatment of mastocytosis has become considerably more practicable in recent years with the availability of agents that directly inhibit mast cells or temporarily reduce their quantity in the skin.