A Review of L-Asparaginase Hypersensitivity in Paediatric Acute Lymphoblastic Leukaemia Patients with Regard to the Measurement of Anti-Asparaginase Antibodies and Their Genetic Predisposition

L-asparaginase is effective as part of the first line childhood acute lymphoblastic leukaemia (ALL) treatment regimen but suffers the risk of antibody production causing immune-mediated sequelae. This article aimed to describe the clinical implication of L-asparaginase hypersensitivity and review the types of antibodies and genetic polymorphisms contributing to it. Clinical or subclinical L-asparaginase hypersensitivity may lead to suboptimum therapeutic effect and jeopardise the clinical outcome in ALL children. Anti-asparaginase antibodies immunoglobulin (Ig)G, IgM and IgE were identified in the L-asparaginase hypersensitivities. Enzyme-linked immunosorbent assay (ELISA) is commonly used to quantify the IgG and IgM levels. The role of IgE in mediating L-asparaginase hypersensitivity is contradictory. Moreover, the presence of antibodies may not necessarily correlate inversely with the L-asparaginase efficacies in some studies. Patients with specific genetic variants have been shown to be more susceptible to clinical hypersensitivity of L-asparaginase. With the advance of technology, gene polymorphisms have been identified among Caucasians using whole-genome or exon sequencing, but the evidence is scanty among Asians. There is lack of pre-clinical study models that could help in understanding the pathophysiological pathway co-relating the gene expression and anti-asparaginase antibody formation. In conclusion, future research studies are required to fill the current gap in understanding the immune mediated reactions towards L-asparaginase upon its administration and its potential impact to the disease outcome.

Magnetic resonance imaging T2* of the pancreas value using an online software tool and correlate with T2* value of myocardium and liver among patients with transfusion-dependent thalassemia major

Objective

Patients with thalassemia major do require lifetime blood transfusions that eventually result in iron accumulation in different organs. We described the usefulness of using magnetic resonance imaging (MRI) T2^*imaging values for the evaluation of pancreatic iron load in these patients, and we correlated it with MRI T2^* haemosiderosis of the myocardium and liver that has been recognized as a non-invasive assessment of iron overload among patients with thalassemia major.

Materials and methods

We conducted a cross-sectional study on 39 patients with thalassemia major in one of the tertiary university hospitals for a 1-year period. Demographic data were collected from the patient's history. MRI T2^* of the pancreas, liver, and heart were executed on all patients in the same setting. Objective values of iron overload in these organs were obtained using the MRI post-processing software from online software.

Results

A total of 32 (82.1%) patients had pancreatic iron overload including 2 patients (5.1%) with severe iron overload and 15 patients (38.5%) with moderate and mild iron overload, respectively. Nine patients (23.1%) had myocardial iron overload, which included 3 patients (7.7%) who had severe cardiac haemosiderosis. Notably, 37 patients (94.9%) had liver iron overload, which included 15 patients (38.5%) who had severe liver haemosiderosis. There was a moderate positive correlation between the relaxation time of the pancreas and heart haemosiderosis (r = 0.504, P < 0.001). No significant correlation was found between the relaxation time of the pancreas with the liver and the heart with the liver.

Conclusion

Pancreatic haemosiderosis precedes cardiac haemosiderosis, which establishes a basis for initiating earlier iron chelation therapy to patients with thalassemia major.

Case report: Kaposi hemangioendothelioma of the right upper limb with the Kasabach-Merritt phenomenon: A potentially lethal diagnostic challenge

Kaposi hemangioendothelioma (KHE) is a rare vascular neoplasm that presents usually within the first year of life. Because of its rarity and complexity, there is often a delay in diagnosis. KHE could be associated with a life-threatening consumptive coagulopathy named the Kasabach-Merritt phenomenon (KMP). Here, we present the case of a 2-month-old girl who presented with progressive redness and swelling of her right upper limb over 6 weeks. Multiple health practitioners misdiagnosed her condition as an insect bite, cellulitis, and necrotizing fasciitis and gave treatment accordingly, which proved futile. A full blood count revealed bicytopenia of anemia and thrombocytopenia, a normal coagulation cascade, low fibrinogen, and raised D-Dimer levels. The imaging was suggestive of a high-flow vascular tumor likely to be a KHE. Subsequently, she was started on single-agent oral sirolimus with a dose increment to achieve satisfactory therapeutic levels and was treated for 1 year. She successfully completed the treatment regimen and had only transient hypertriglyceridemia, which resolved upon the completion of treatment. Currently, she is in remission 3 years after treatment. Keeping her case as an example, we would like to highlight the potentially lethal misdiagnosis of KHE with KMP, the importance of an early diagnosis of this condition, and the successful treatment outcome with single-agent sirolimus.

Efficacy of Granisetron in the Prevention of Nausea and Vomiting among Paediatric Oncology Patients Receiving Moderate to Highly Emetogenic Chemotherapy: A Single-Blinded, Non-Inferiority Trial

This single-blinded, non-inferiority trial was conducted over an 8-month period to examine the efficacy of intravenous granisetron at two differing doses in preventing acute and delayed chemotherapy-induced nausea and vomiting (CINV)among paediatric patients receiving moderate to highly emetogenic chemotherapy. Seventeen patients (9 males and 8 females) were recruited and randomly assigned to receive alternating granisetron dosages of 0.01 mg/kg and 0.04 mg/kg during each chemotherapy cycle. The severity of CINV during and three days post-completion of chemotherapy, as well as common side effects of granisetron were recorded. A total of 78 cycles of chemotherapy (38 cycles of 0.01 mg/kg and 40 cycles of 0.04 mg/kg) were evaluated. The median age of the study population was 5.2 years (interquartile range 25th, 3.8; 75th, 8.7). Patients’ diagnoses comprised of haematological malignancy, bone tumour and cerebral neoplasm. From this study, we demonstrated that intravenous (IV) granisetron 0.01 mg/kg was non-inferior to 0.04 mg/kg in terms of achieving a complete response for acute CINV. However, a similar observation was not seen in the post-treatment period analysis (delayed CINV). In conclusion, IV granisetron at 0.04 mg/kg/dose provides effective protection and prophylaxis of both acute and delayed CINV. Further study with a larger sample size may be required before a definite conclusion can be made with regards to efficacy of 0.01 mg/kg dose.

Siriraj I Gγ(Aγδβ)0-thalassaemia causing severe thalassaemia intermedia in compound heterozygous state with IVS1-1(G→T) mutation

The Siriraj I ^Gγ(^Aγδβ)⁰-thalassaemia is a novel mutation involving a 118kb deletion of the β-globin gene cluster. It was first reported in 2012 in two unrelated families from the southern part of Thailand. The carriers in the heterozygous state are clinically asymptomatic. Nonetheless, its complex interaction with other β-thalassaemia could give rise to different clinical phenotypes, ranging from mild thalassaemia intermedia to thalassaemia major. We report here a case of a six-year-old Malay boy, presented with pallor, growth failure and hepatosplenomegaly. His haemoglobin at presentation was 9.2g/dL with a mean cell haemoglobin of 22.6pg and a mean cell volume of 69.9fl. His peripheral blood smear showed features of thalassaemia intermedia. Haemoglobin (Hb) analysis revealed markedly raised Hb F (83%), normal HbA2 levels and absent HbA. Deoxyribonucleic acid (DNA) analysis showed compound heterozygous IVS1-1 (G→T) β-globin gene mutation and Siriraj I ^Gγ(^Aγδβ)⁰-deletion (genotype β^IVS1-1/ β ^{Siriraj I deletion}). Both his father and elder sister are carriers of Siriraj I ^Gγ(^Aγδβ)⁰-thalassaemia while his mother carries IVS1-1 (G→T) gene mutation. Clinically, the patient is transfusion dependent on six weekly regime. To the best of our knowledge, this is the first reported case in Malaysia involving unique Siriraj I ^Gγ(^Aγδβ)⁰-thalassaemia and IVS1-1 (G→T) in a compound heterozygous state. In summary, detection of Siriraj I ^Gγ(^Aγδβ)⁰-thalassaemia is essential as this deletion can lead to severe disease upon interaction with a β-thalassemia point mutation as demonstrated in our case. The establishment of effective carrier screening and genetic counselling is important to prevent its adverse consequences.

Case Report: The Use of Intravenous SMOFlipid Infusion to Treat Severe Asparaginase-Induced Hypertriglyceridemia in Two Pediatric Acute Lymphoblastic Leukemia Patients

Asparaginase-induced hypertriglyceridemia can have a spectrum of clinical presentations, from being asymptomatic to having life-threatening thrombosis or hyperviscosity syndrome. At present, there is no recommendation on routine lipid monitoring during asparaginase-containing treatment phase, nor a standardized guideline on its management. Two cases are presented here to illustrate the effects of concurrent infection on asparaginase-induced hypertriglyceridemia in patients with high-risk ALL and the use of SMOFlipid infusion as a treatment option in an acute situation.

LINC-31. TREATMENT OUTCOME IN CHILDREN WITH MEDULLOBLASTOMA IN MEDIUM-INCOME COUNTRY: AN EXPERIENCE FROM A SINGLE TERTIARY CENTRE IN KUALA LUMPUR, MALAYSIA

INTRODUCTION

Medulloblastoma is the most common malignant brain tumour in children. The overall outcome has improved however, this was not translated to developing nations.

METHOD

This was a retrospective review of patients from January 2000 to December 2017. Treatment was given using modified SIOP PNET 4 protocol: cranio spinal irradiation (CSI), a total of 54G with vincristine followed by 8 cycles of adjuvant chemotherapy. Prior to year 2007, patients had CSI with or without adjuvant chemotherapy. Those &lt;3 years old received modified UKCCSG/SIOP CNS protocol with 2 weekly chemotherapy for a duration of 392 days followed by CSI when required. All patients had MRI brain and spine, and tissue histopathological examination but without molecular subtype.

RESULTS

Medulloblastoma comprised of 30% (n=31) out of total 103 brain tumour cases. Mean age at presentation was 7.6 years old (SD 4.4) with male to female ratio of 2:1. Average time of symptoms was 4.8 weeks. Majority, 77.4% was high risk and 19.4% was standard risk. There was high treatment abandonment rate (35.5%, n=11). Three patients returned and completed treatment after multiple surgeries in an average of 9 months. Three years OS and EF were 69.6% and 74.8%, respectively. Six patients aged &lt; 3years; half had advance disease on palliative care post surgery. Other survivors had severe learning difficulty and two had second malignancy (meningioma and thyroid carcinoma) at average 15.5 years after diagnosis.

CONCLUSION

Strategy to reduce treatment abandonment is crucial. Moreover, multidisciplinary management and molecular stratification are important in improving the outcome.

LINC-27. PAEDIATRIC SUPRASELLAR TUMOURS: CLINICAL EXPERIENCE FROM A SINGLE TERTIARY CENTRE IN KUALA LUMPUR, MALAYSIA

INTRODUCTION

The outcome of suprasellar tumours in children varies with the diagnosis and morbidity is significant. We herein report the clinical features of children with suprasellar tumours treated at our centre.

METHODS

Clinical data were collected by retrospective review from January 2000 to December 2019. The patients were identified from the paediatric haematology and oncology unit registry.

RESULTS

There was a total of 103 children with brain tumour and suprasellar tumours comprise of 14.6% (n=15). Median age at presentation was 7 years old. Male to female ratio was 3:2. Majority of cases was low grade glioma, 40% (n=6) and germ cell tumour(GCT) 33.3% (n=5) followed by craniopharyngioma, 13.3% (n=2) and Rathke cleft cyst, 6.7% (n=1). All patients had tissue diagnosis except one with secreting GCT and one with unsatisfactory tissue sample. Mean duration of follow up was 7.4 years. One patient with germinoma was lost to follow-up after radiotherapy. Three out of 13 (23%) patients died; 2 with GCT from disease progression; 1 craniopharyngioma after 11 years of unknown cause. All survivors have significant morbidity; 70% have moderate to severe visual impairment, 90% have at least two pituitary hormones deficiency, 20% have neurological deficit and 1 was surgically related. Two boys have precocious puberty not related to disease progression. Two with GCT with diabetes insipidus had history of thromboembolism (stroke and pulmonary embolism).

CONCLUSIONS

Suprasellar tumours in children at our centre pose a significant long-term complications and multidisciplinary team management and follow up is required to improve the morbidity.

Primary extragonadal vaginal yolk sac tumour: A case report

INTRODUCTION

Yolk sac tumour (YST) or endodermal sinus tumour is rare and typically seen in gonads.

CASE REPORT

We described a case of extragonadal vaginal YST in a one year and seven months old girl who presented with vaginal discharge and bleeding, and discuss its differential diagnosis and potential pitfalls in immunohistochemistry. She was found to have a suprapubic mass on examination. The serum alpha fetoprotein was 11919.4 ng/mL. Computed tomography of the pelvis revealed a large 6.4 cm heterogenous pelvic mass. Colposcopic examination of the pelvis showed a fungating vaginal mass that was subsequently confirmed as a yolk sac tumour. Immunohistochemically, the malignant cells were positive toward CKAE1/AE3, AFP and glypican-3, as well as CD117.

DISCUSSION

Solid pattern extragonadal vaginal YST may morphologically resemble dysgerminoma that is also CD117 positive, while the glandular pattern YST may have clear cytoplasm and is positive for cytokeratin; hence, may resemble clear cell carcinoma. Being mindful of these potential diagnostic caveats is necessary to prevent misdiagnosis.

Correlation between MRI characteristics of medulloblastoma with histopathological subtypes and 2-year survival

Objectives:

The objective of this study is to describe the imaging features of medulloblastoma (MB) and correlate the MR characteristics with the different histological subtype of MB with 2-year survival.

Materials and Methods:

This is a retrospective descriptive study. A total of 29 patients diagnosed with MB from January 2005 to December 2015 were included in this study. The MRI brain and spine studies of these patients were retrieved and reviewed by a pediatric radiologist and a neuroradiologist independently, both blinded from the histological type of the MB. The HPE slides were also retrieved and reviewed by a pathologist.

Results:

80% of desmoplastic MB showed the presence of intracranial leptomeningeal seeding and 57.1% of anaplastic MB showed the presence of necrosis. The presence of intracranial leptomeningeal seeding (P = 0.002) and necrosis (P = 0.019) was predictive of the histological subtypes. There is a significant correlation between the enhancement pattern and the 2-year outcome (P = 0.03) with 6 out of 8 patients whose tumors showed minimal enhancement having disease progression within 2 years. A significant correlation was also seen between the presence of necrosis with a poorer outcome (P = 0.03) and between the HPE subtype and 2-year outcome (P = 0.03) with anaplastic MB having the poorest prognosis.

Conclusion:

MR imaging features of intracranial leptomeningeal seeding and the presence of necrosis were correlated with a specific histologic subtype of MB. The enhancement pattern as well as necrosis correlated with 2-year poorer outcome of the disease.

Early Surgery Is Feasible for a Very Large Congenital Infantile Fibrosarcoma Associated With Life Threatening Coagulopathy: A Case Report and Literature Review

Background: Congenital infantile fibrosarcoma (CIF) is a rare malignant soft tissue tumor that predominantly occurs in children under 1 year of age. CIF is frequently misdiagnosed with other conditions like hemangioma of infancy, infantile fibromatosis, or kaposiform hemangioendothelioma. Disseminated intravascular coagulopathy (DIVC) is rarely reported to be associated with CIF. Case presentation: We describe an infant who presented with a large mass over the right arm. She was initially treated conservatively as hemangioma but was later confirmed by tissue histopathological examination to have CIF as the mass rapidly increased in size. She developed massive intra-tumoral bleed with DIVC whilst receiving neoadjuvant chemotherapy requiring multiple blood products transfusion. An urgent near-total resection of the tumor was performed in view of life threatening bleeding despite multiple blood transfusions. Post-operatively, she received further adjuvant chemotherapy. Subsequently, she remained in complete remission 32 months off-treatment and has full function of the affected limb. Conclusions: CIF is an important condition to be considered in infant who has large mass over the extremity. DIVC could be associated with large CIF and when it occurs can be life-threatening. Whenever feasible early surgery should be performed in very young patients with large CIF to prevent mortality from bleeding.

Transition care readiness among patients in a tertiary paediatric department

INTRODUCTION

A smooth transition of healthcare for young people with chronic illnesses from paediatric to adult healthcare services is important to ensure optimal outcome. At the moment, there are no standard guidelines to assess a patient's readiness to transfer care.

METHODS

A cross-sectional study using a self-administered questionnaire, adapted from UNC (University of North Carolina) TRxANSITION self-assessment tool was conducted to evaluate patients' transition care readiness in paediatric haematology and paediatric diabetes clinic.

RESULTS

A total of 80 patients (37 thalassaemia and 43 diabetes) with the mean age of 21.2 (SD±4.3) years, were recruited during the 3-month study period. Majority of the patients have basic knowledge regarding their medications, and were able to comply with their follow-up. The mean total score obtained by the respondents on this questionnaire was 15.3 (SD±3.59). Self-management skills and knowledge on disease were the two poorly scored section; with mean score of 3.78 (SD±1.38) and 4.28 (SD±1.20) respectively. Overall, only 21 (26.2%) respondents obtained high score (score above 75th percentile). Seventy-five percent of the respondents admitted that they were not ready for transfer to an adult healthcare service yet at the time of the study.

CONCLUSION

We suggest that patients with high score should be prepared for transition to adult facility whereas those with a low score need to be identified to ensure provision of continuous education.

Acquired thrombotic thrombocytopenia purpura associated with severe ADAMTS13 deficiency in a 3-year-old boy: a case report and review of the literature

Background

Acquired thrombotic thrombocytopenia purpura is very rarely encountered in children. It is often misdiagnosed initially when the condition is not inherited.

Case presentation

We describe a 3-year-old Malay boy who presented with simple febrile seizure and had no neurological deficit, however, he was found to have microangiopathic hemolytic anemia, thrombocytopenia, and elevated serum lactate dehydrogenase. An ADAMTS13 assay results showed zero activities (0%), and markedly high level of ADAMTS13 inhibitor (93.15 U/mL) confirming the diagnosis of secondary thrombotic thrombocytopenia purpura. He received fresh frozen plasma infusions for 3 days and subsequently his platelet levels normalized. Serial ADAMTS13 assay results showed improvement. He was also given a short course of prednisolone after which the ADAMTS13 activity normalized (> 114%) at the end of prednisolone course.

Conclusions

At presentation, acquired thrombotic thrombocytopenia purpura in a very young child is commonly misdiagnosed as other conditions like idiopathic thrombocytopenic purpura, Evans syndrome, atypical hemolytic-uremic syndrome, or malignancy. ADAMTS13 assay should be performed early when thrombotic thrombocytopenia purpura is suspected as this condition is associated with dire consequences.

Diagnostic challenge of Burkitt's lymphoma at early age

A four-year-old Ibanese boy presented with subacute abdominal distension for two months duration. Ultrasound and computed tomography (CT) scan showed solid liver masses as well as bowel and intraperitoneal lesions. Initial diagnosis of intraperitoneal inflammatory process as in tuberculosis with non-liquefied liver abscess with differential diagnosis of neoplastic process was made. Liver biopsy and peritoneal fluid analysis revealed Burkitt's lymphoma (BL). We aim to highlight the diagnostic challenge of BL in this young age group emphasizing on the ultrasound and CT features of intraabdominal BL. We would also want to stress the importance of early diagnosis of BL as it is known to be the most aggressive tumour within 24 hours yet to have good survival if early diagnosis was made.

Hb lepore/β0-thalassaemia with α+-thalassaemia interactions, a potential diagnostic pitfall

Haemoglobin (Hb) Lepore is a variant Hb consisting of two α-globin and two δβ-globin chains. In a heterozygote, it is associated with clinical findings of thalassaemia minor, but interactions with other haemoglobinopathies can lead to various clinical phenotypes and pose diagnostic challenges. We reported a pair of siblings from a Malay family, who presented with pallor and hepatosplenomegaly at the ages of 21 months and 14 months old. The red cell indices and peripheral blood smears of both patients showed features of thalassaemia intermedia. Other laboratory investigations of the patients showed conflicting results. However, laboratory investigation results of the parents had led to a presumptive diagnosis of compound heterozygote Hb Lepore/β-thalassaemia and co-inheritance α+-thalassaemia (-α3.7). Hb Lepore has rarely been detected in Southeast Asian countries, particularly in Malaysia. These two cases highlight the importance of family studies for accurate diagnosis, hence appropriate clinical management and genetic counseling.

Parental reports of behavioural outcome among paediatric leukaemia survivors in Malaysia: a single institution experience

OBJECTIVES

To determine the behavioural impact of chemotherapy in survivors of acute lymphoblastic leukaemia (ALL) treated with chemotherapy only and to identify treatment-related or sociodemography-related factors that might be associated with behavioural outcome.

METHODS

We examined 57 survivors of childhood ALL, who were off treatment for at least 2 years and were in remission, aged 4-18 years, and 221 unrelated healthy controls. The Child Behaviour Checklist (CBCL) parent report was used either in English or in Bahasa Malaysia (the national language of Malaysia) to assess the behavioural outcome.

RESULTS

Childhood ALL survivors had significantly higher scores on externalising behaviour on the CBCL parent report than did controls. Higher problem scores were found in ALL survivors with single parents on 'total problems' (P = 0.03) and subscales 'withdrawn' (P = 0.03), 'social problems' (P < 0.01) and 'delinquent behaviour' (P = 0.03) than in survivors with married parents. Significant associations were seen between a lower education level of the father and the variables representing internalising (withdrawn, anxious/depressed) and externalising (aggressive behaviour). We observed trends on higher scores in all scales in ALL survivors with single parents than in controls with single parents or with fathers with low education level, especially primary education only.

CONCLUSIONS

Malaysian childhood ALL survivors had a significantly increased risk for externalising behavioural problems, and there was a trend towards increased risk of problems in many other behavioural scales. Understanding the sociocultural dimension of patients' health is important to be able to design the most appropriate remedy for problem behaviours detected in this multi-ethnic population.

A case series of α-thalassemia intermedia due to compound heterozygosity for Hb Adana [HBA2: c179G>A (or HBA1); p.Gly60Asp] with other α-thalassemias in Malay families

Hb Adana [HBA2: c179G>A (or HBA1); p.Gly60Asp] is a rare hemoglobin (Hb) variant due to a mutation at codon 59 of the α2- or α1-globin gene resulting in a glycine to aspartic acid substitution. Two siblings with a unique coinheritance of Hb Adana and Hb Constant Spring (Hb CS, α142, Term→Gln, TAA>CAA; HBA2: c.427 T>C) (α(codon 59)α/α(CS)α), were compared phenotypically with another two siblings carrying the Hb Adana mutation and a 3.7 kb deletion (α(codon 59)α/-α(3.7)). Although they all had α-thalassemia intermedia (α-TI), the former were clinically more severe than the latter. The first pair of siblings presented at a much younger age than the second pair and showed lower Hb levels and significant extramedullay hemopoiesis. Another case of a hydropic fetus as a result of Hb H/Hb Adana is also described. Their clinical phenotypes and hematological parameters are all presented for comparison.

Extramedullary hematopoiesis simulating posterior mediastinal tumors

We report the case of a patient with intrathoracic extramedullary hematopoiesis presenting as a posterior mediastinal tumor in response to chronic hemolytic anemia. Noninvasive studies including chest roentgenograms, computed tomographic scans, magnetic resonance images, and nuclear scans can establish the diagnosis in most cases. In equivocal cases, transthoracic needle biopsy and open biopsy should be considered. Surgical resection is recommended only for patients with symptoms of compression.

An improved method for localization of nonpalpable breast lesions

Insertion of a hooked stylet into the region of a mammographic abnormality is a simple method of localization prior to biopsy. The hook on the stylet does not permit movement of the localization device away from the lesion during the interval between placement and surgical excision. A xeroradiograph of the biopsy specimen determines whether the suspected region was obtained surgically.

The roentgen diagnosis of pelvic extraperitoneal effusion

Extraperitoneal, perivesical pelvic effusions may be hemorrhagic or uriniferous, the latter resulting from extraperitoneal rupture of the bladder or disruption of the posterior urethra. The effusions may be recognized on anteroposterior radiographs of the pelvis by (a) displacement of the bladder (small effusion); (b) obliteration of the normal soft-tissue anatomy within the pelvis (moderate effusion); and (c) upward displacement of the pelvic ileal loops and extension of the effusion into the flank stripes (large effusion). Perivesical effusions most frequently accompany anterior pelvic arch injuries, i.e., double vertical and Malgaigne fractures and fractures involving, or separation of, the pubic symphysis.

Interactions of diphenylhydantoin and cardiac glycosides on atrial potassium

Effects of diphenylhydantoin (DPH) on amphibian atrial myocardium K were investigated using a method which permits both total tissue K and tension response to be monitored continuously. In normal (nondigitalized) preparations, DPH caused a decrease in average K efflux, a net gain of tissue K, and negativeinotropy at low perfusate K concentrations. However, the DPH-induced gain of tissue K was abolished at high perfusate K concentrations while marked negative inotropy was still observed. It is concluded that a gain of tissue K is not the cause of DPH-induced negative inotropy. When digitalis-induced inotropy was associated with tissue K loss, DPH reversed tissue K loss and positive inotropy and caused a decrease in average K efflux. In the presence of toxic effects of digitalis, DPH reversed the K loss and the contracture, but the loss of developed tension was not reversed by DPH. Transmembrane resting potentials and action potential duration were reduced by digitalis and were returned to or above control levels in the presence of DPH. The present findings are consistent with the hypothesis that the therapeutic effect of DPH in digitalis toxicity is brought about by an inhibition of K efflux. This would tend to minimize the loss of tissue K which results from sodium pump inhibition.