Primary Atomic Frequency Standards at NIST

The development of atomic frequency standards at NIST is discussed and three of the key frequency-standard technologies of the current era are described. For each of these technologies, the most recent NIST implementation of the particular type of standard is described in greater detail. The best relative standard uncertainty achieved to date for a NIST frequency standard is 1.5×10(-15). The uncertainties of the most recent NIST standards are displayed relative to the uncertainties of atomic frequency standards of several other countries.

MR imaging in children with dermatomyositis: musculoskeletal findings and correlation with clinical and laboratory findings

OBJECTIVE

The purpose of this study was to describe the musculoskeletal MR findings in childhood dermatomyositis and to correlate MR findings with indicators of disease activity such as muscle strength and serum levels of muscle enzymes.

SUBJECTS AND METHODS

This prospective study included 24 children: 19 children with dermatomyositis and five control subjects. The diagnosis of dermatomyositis was established by clinical findings and serum levels of muscle enzymes in all patients, electromyography in six patients, and biopsy in four patients. At the time of the initial MR evaluation, patients were classified on the basis of clinical findings as having active (n = 15) or inactive (n = 4) disease. A total of 44 MR evaluations of patients with dermatomyositis were included in the study: 19 initial MR examinations and 12 examinations repeated after 4-6 months of therapy in patients with active disease. An additional 13 examinations were performed on five patients. Conventional T1-weighted (SE 600/20) and T2-weighted (SE 2500/80) spin-echo and fat-suppressed MR images were obtained. The T2-weighted images (TE = 80) were used for comparison. In addition to the visual assessment, ratios between the signal intensity of muscles (gluteus, adductors, quadriceps, and hamstrings) and the signal intensity of subcutaneous fat in the same tomographic section were calculated.

RESULTS

All patients with clinically active disease (n = 15) had abnormal findings on MR studies, whereas those with inactive disease (n = 4) had normal MR findings. Signal-intensity ratios of patients with active disease were greater than those in control subjects, whereas the ratios in patients with inactive disease were not different from those in control subjects. After 4-6 months of therapy, the average signal-intensity ratios of treated patients with repeated MR evaluations (n = 12) differed from ratios obtained before therapy in the same patients, but were not different from the ratios in control subjects. Other MR findings observed were perimuscular edema, enhancement of the chemical-shift artifact, and inflammatory changes of subcutaneous fat. Fat-suppressed imaging enhanced visualization of abnormalities. Markedly abnormal signal intensities of muscle were associated with marked elevations of serum levels of muscle enzymes; however, abnormal MR findings were visualized with normal serum levels of muscle enzymes.

CONCLUSION

Findings of active childhood dermatomyositis on T2-weighted MR images include increased signal intensity in affected muscle, perimuscular edema, enhanced chemical-shift artifact, and increased signal intensity in subcutaneous fat. After therapy, signal intensity of muscle returns to normal. These MR findings are enhanced on fat-suppressed images.(ABSTRACT TRUNCATED AT 400 WORDS)

Atrioventricular conduction in children of women with systemic lupus erythematosus

The neonatal lupus syndrome consists of transient cutaneous lupus lesions or permanent congenital complete heart block (or hepatic fibrosis), or both, in infants born to mothers with systemic lupus erythematosus (SLE). The frequency of conduction abnormalities was examined in 86 offspring of 53 women affected by SLE. Electrocardiograms from the offspring demonstrated normal sinus rhythm in 84 of 86 offspring. The PR interval was normal for age (< 95th percentile) in 82 offspring and normal for heart rate in 81. Three children had a PR interval > 95th percentile (i.e., first-degree heart block) for both age and heart rate. The PR interval of the other 6 subjects with first-degree heart block for age or heart rate (> or = 95th percentile) was < or = 0.18 second. In contrast, using a rank assignment of PR intervals in relation to heart rate and age derived from published standards, grouped data indicated that heart rate adjusted for age was greater and PR interval adjusted for heart rate longer in offspring of mothers who had the onset of SLE before or during pregnancy than in the normal population; this observation did not hold for offspring whose mothers developed SLE after the pregnancy. These findings indicate that offspring of mothers with SLE, even in the absence of an abnormal electrocardiogram, may have experienced a maternal internal environment that produces subclinical changes in atrioventricular conduction. However, newborns with a normal pulse rate are unlikely to have significant abnormalities in atrioventricular conduction and do not need screening electrocardiograms at birth.

Fat-suppressed MR imaging of myositis

A hybrid fat-suppression sequence in magnetic resonance (MR) imaging was used to evaluate inflammatory muscle disorders in seven children: five patients with dermatomyositis, one patient with vasculitis, and one patient with viral myositis. Fat-suppressed multisection axial images obtained with the same repetition and echo times as those used to obtain standard spin-echo (SE) images enabled direct comparison of images, with little variation of T1 and T2 weighting. In six patients, the contrast on images obtained with T2 fat suppression was 15%-20% greater than contrast on conventional T2-weighted SE images. In all seven patients, the subjective judgment was that T2-weighted fat-suppression sequences improved visualization of muscle abnormalities. It is concluded that T2 fat suppression is useful in evaluation of inflammatory muscle disorders in children because it increases contrast and eliminates fat as a cause of muscle abnormality.

Serial magnetic resonance imaging in juvenile dermatomyositis

Magnetic resonance imaging (MRI) was used to follow the course of juvenile dermatomyositis from the onset of disease through resolution of a primary relapse. The signal intensity of the T2-weighted image of involved muscles was elevated during periods of disease activity, and returned to approximately normal levels with effective suppression of disease activity. T1-weighted images of involved muscles remained approximately normal despite disease activity.

Carpo-metacarpal growth disturbance and the assessment of carpal narrowing in children with juvenile rheumatoid arthritis

Second metacarpal length (M2), radio-metacarpal length (RM), and intermetacarpal width (W) were measured on 96 radiographs in 52 children with polyarticular juvenile rheumatoid arthritis (JRA), and compared with body height and skeletal maturation in order to: (1) differentiate between processes resulting in retardation of bone growth and those producing delay in skeletal maturation; (2) assess the severity and progression over time of such retardation; and (3) assess the impact of retardation of the second metacarpal on the assessment of carpal narrowing in children with JRA. All measurements were converted into z scores (the units of standard deviation above or below the normal mean for each measurement) based on published norms. Retardation of M2 (mean z scores -0.91) began earlier and was more severe compared with retardation of height (mean z score -0.25). This disproportion widened with increasing duration of disease. That this primarily represents a disturbance in M2 growth rather than a secondary effect due to altered maturation is suggested by the bone ages being normal (mean z score 0.14) and the absence of premature closure of the metacarpal physes. Z scores for RM/W (mean -3.53) were at least 1 Z more negative than for corresponding measurements of RM/M2 (mean -2.41) in 47 (90.4%) children and the mean difference between the z scores for RM/W was -1.12. This discrepancy between RM/W and RM/M2 was eliminated by correcting for the reduction in M2.

Distal interphalangeal joint abnormalities in children with polyarticular juvenile rheumatoid arthritis

Involvement of the distal interphalangeal (DIP) joints was noted radiographically in 24 (43.6%) of 55 patients with polyarticular juvenile rheumatoid arthritis. DIP changes were apparent later in the course of the disease and were less severe than in other affected joints. Soft tissue swelling and joint space narrowing were the most frequent abnormalities in the DIP joints. Erosive changes and angular deformities were uncommon. There was no significant correlation between DIP joint involvement and sex, age at presentation, involvement of the hands and wrists at presentation, or positivity of either rheumatoid factor or antinuclear antibody. There was a strong correlation between the presence of extraarticular signs and symptoms and involvement of the DIP joints; however, this may reflect the greater severity of the disease in these patients generally.

Magnetic resonance imaging appearance of the muscles in childhood dermatomyositis

Documentation of muscle involvement in a child thought to have dermatomyositis may require the performance of invasive procedures such as electromyography and/or muscle biopsy. We describe four patients with dermatomyositis in whom magnetic resonance imaging (MRI) demonstrated the muscle involvement. The involved muscles had increased signal intensity on the T2-weighted images (SE 2500/80) and normal appearance on the T1-weighted images (SE 600/20). The involvement of the muscles was not uniform. There was good correlation between the distribution of muscle involvement by MRI and functional testing. Follow-up MRI scans in patients with favorable outcome demonstrated that the affected muscles had returned to normal signal intensity. Although the MRI findings are not specific, in the proper clinical context they may be helpful in establishing the diagnosis of dermatomyositis. MRI may also be used in establishing an appropriate muscle biopsy site. In addition, MRI may be used for monitoring the progress of the disease.

Children with juvenile rheumatoid arthritis at school. Functional problems, participation in physical education. The implementation of Public Law 94-142

Parents of 135 children with juvenile rheumatoid arthritis (JRA) completed a mailed questionnaire about problems at school. Writing was the most frequently reported difficulty, with hand involvement causing more problems than decreased mobility. Compared to children with pauciarticular JRA, those with polyarticular or systemic JRA were significantly more likely to miss school, experience problems, participate less in physical education, have an Individualized Educational Plan (IEP) developed, and receive related services. Only 39 parents had heard of PL 94-142, and only 21 of those could define the federal law. Twenty children had an IEP within the previous two years. Possible deficiencies in the implementation of PL 94-142 were discovered. This study demonstrates that the treatment of children with JRA should include efforts to: 1) identify and remediate potential performance limitations before they become problematic at school; 2) communicate this information to parents and school personnel; 3) and improve parents' awareness and understanding of PL 94-142.

The NIST Automated Computer Time Service

The NIST Automated Computer Time Service (ACTS) is a telephone time service designed to provide computers with telephone access to time generated by the National Institute of Standards and Technology at accuracies approaching 1 ms. Features of the service include automated estimation by the transmitter of the telephone-line delay, advanced alert for changes to and from daylight saving time, and advanced notice of insertion of leap seconds. The ASCII-character time code operates with most standard modems and computer systems. The system can be used to set computer clocks and simple hardware can also be developed to set non-computer clock systems.

Factor VIII related antigen and childhood rheumatic diseases

Factor VIII related antigen (FVIIIRAg) levels were measured in the plasma of 63 children with rheumatic diseases and 20 controls. High levels were found in patients with systemic juvenile arthritis, systemic lupus erythematosus, dermatomyositis and systemic forms of vasculitis. The amount of circulating FVIIIRAg seemed to be independent of values for erythrocyte sedimentation rate, C-reactive protein and fibrinogen, implying that it was not just another acute phase reactant. Rather, a high level of circulating FVIIIRAg most likely reflects the presence of vascular endothelial injury, and this test may be useful in monitoring disease activity in children with rheumatic diseases in which vasculitis is present.

Juvenile dermatomyositis: histological findings and pathogenetic hypothesis for the associated skin changes

Skin biopsies from patients with scleroderma and juvenile dermatomyositis (DM) share many histologic features. Characteristics common to both diseases are particularly evident in the dermal microvasculature and include endothelial swelling and concentric thickening of the vascular basement membrane. Biopsies performed on 3 patients with the severe vasculitic form of juvenile DM showed these changes as well as dropout of vessels and linear deposition of collagen. The latter findings, seen late in the course of the disease, are indistinguishable from those of advanced scleroderma. A hypothesis is presented which attempts to relate these histological findings to a common underlying pathophysiologic mechanism.

HLA-DR and MT associations with the clinical and serologic manifestations of pauciarticular onset juvenile rheumatoid arthritis

Significant HLA-DR and MT associations were observed with certain clinical and serologic manifestations of pauciarticular onset juvenile rheumatoid arthritis (PO-JRA). An increase in the MTI frequency was found in 56 children with PO-JRA in comparison to 95 normal controls. This association was limited to children with a younger age of onset (less than 6 years) and a persistent pauciarticular course. An increase in HLA-DRW8 and a decrease in DR4 were associated with a younger age of onset and antinuclear antibody (ANA) seropositivity. In addition, an increased frequency of DR5 was seen in ANA positive children. All of these HLA-DR and MT associations were independent of coassociating Ia specificities.

Patterns of calcification in childhood dermatomyositis

The radiographs of 40 patients with childhood dermatomyositis, an uncommon inflammatory disease, were reviewed. Four distinct patterns of calcification were identified: deep calcareal masses, superficial calcareal masses, deep linear deposits, and a lacy, reticular, subcutaneous deposition of calcium encasing the torso (not emphasized in recent literature). This linear reticular pattern of calcification was associated with a severe unremitting clinical course. Soft-tissue calcification was identified in 40% of cases, a lower incidence than previously reported. No patient in this series had acroosteolysis or pulmonary parenchymal disease, radiographic findings more commonly associated with childhood scleroderma.

Childhood dermatomyositis: factors predicting functional outcome and development of dystrophic calcification

The medical records of 47 children with dermatomyositis who were seen in the pediatric rheumatology clinic at the University of Michigan between 1964 and 1982 were reviewed. Although most children with dermatomyositis have a good prognosis, the best predictor of both good functional recovery and minimal calcinosis is early treatment after the onset of symptoms, using high doses of prednisone for an adequate length of time. Of the children given such treatment, 78% had good functional outcomes, and disabling calcinosis was seen in 20% or less. Children given treatment late in the course of disease and with low doses of steroids are more likely to be functionally limited and have a greater amount of dystrophic calcium salt deposition. In our study, only 33% of patients given such treatment had a mild disease course with good functional outcome. We have identified a subgroup of children with dermatomyositis who appear to do poorly despite optimal therapeutic regimens. These patients are distinguished by a severe disease course responding minimally to corticosteroid therapy and manifested by persistent muscle weakness, elevations of muscle enzyme activity, and severe generalized cutaneous vasculitis. These children are at high risk for the development of exoskeleton-like calcification; consideration should be given to combined immunosuppressive therapy early in the course of disease.

Radiographic findings of scleroderma in childhood

The radiographs of 12 children with the American Rheumatism Association criteria for scleroderma were analyzed and compared to the adult presentation. Childhood and adult manifestations of the disease differ. Although some similarities exist, tuft resorption and soft-tissue calcifications in the fingers are more common in childhood. In contrast, small bowel involvement, hand contractures, and erosive arthropathy are less frequent. In particular, inflammatory joint destruction was not identified in this small pediatric group.

Immunogenetic studies of juvenile dermatomyositis. HLA antigens in patients and their families

Typing for HLA-A and -B antigens was performed on 87 children with definite juvenile dermatomyositis (JDMS). A significantly increased frequency of HLA-B8 (estimated relative risk = 2.8, Pc less than 0.01) was observed among White patients, but not among Blacks or Latin Americans with JDMS. No abnormality of HLA haplotype segregation was observed among 38 healthy siblings of the JDMS probands.

Mucha-Habermann disease in children -- the association with rheumatic diseases

Two children are described who developed Mucha-Habermann disease as infants. One boy had juvenile rheumatoid arthritis that ran a progressive course over 10 years, although his skin disease responded to a low dose of corticosteroids. One girl had polyarthritis associated with onset of her rash but both resolved over several years without treatment. She has since developed scleroderma followed by a reappearance of her skin lesions.

Renal papillary necrosis in juvenile rheumatoid arthritis

Three patients who developed renal papillary necrosis while receiving long-term, high-dose aspirin therapy for juvenile rheumatoid arthritis are presented. It appears that aspirin alone or aspirin in combination with other drugs is the causative agent. The incidence and biologic significance of renal papillary necrosis are insufficient to alter the use of aspirin as the drug of choice in management of JRA. It is recommended that all children with JRA be encouraged to drink ample fluids and be followed with periodic urinalysis and blood pressure measurements. Those children who develop hematuria or hypertension should be evaluated by excretory urography.

The clinical progression of apparent juvenile rheumatoid arthritis to systemic lupus erythematosus

Ten patients with juvenile rheumatoid arthritis (JRA) developed clinical manifestations of systemic lupus erythematosus (SLE) in 2 1/2 to 21 yr. At onset there was little to distinguish these patients from other children with JRA. Chronic arthritis developed in all and was not different from that seen in JRA. Onset of SLE followed a flare of arthritis in 8 patients, development of serositis in 5, and fever and rash in 5. LE cells and elevated DNA-binding were found in all patients, and glomerulonephritis was demonstrated in the 6 patients on whom renal biopsies were done. This group of patients may represent an important diagnostic subset of children with JRA or SLE.

The association of autoimmune diseases and anti-IgA antibodies in patients with selective IgA deficiency

The prevalence of antibodies to immunoglobulin A (IgA) was studied in eighty-three subjects with selective IgA deficiency (SIgAD), thirty-three normal individuals, thirty-two children with juvenile rheumatoid arthritis (JRA) and normal or elevated IgA, seventeen children with systemic lupus erythematosus (SLE) and normal or elevated IgA, and thirteen patients with hypogammaglobulinaemia. Anti-IgA antibodies were detected by haemagglutination of human erythrocytes coated with one of two IgA myelomas by the chromic chloride technique. Antibodies to IgA were not found in significant titre in individuals with normal or elevated IgA or in those with hypogammaglobulinaemia. In IgA deficient patients, elevated titres were found in 25--30% of those who were healthy or who had non-rheumatic diseases, 50% of those with rheumatoid arthritis, 77% of those with JRA and 100% of those with SLE. Patients with rheumatic diseases and SIgAD may therefore be particularly at risk of developing anti-IgA-mediated reactions to blood products.

Diagnostic significance of antibody to native deoxyribonucleic acid in children with juvenile rheumatoid arthritis and other connective tissue diseases

Sera of children with juvenile rheumatoid arthritis and other connective tissue diseases were tested for antibodies to native DNA by a radiolabeled-binding assay. Normal values were obtained in 130 children with JRA, including 28 with uveitis and 14 with selective IgA deficiency. Normal values were also found in sera from children with dermatomyositis, scleroderma, polyarteritis, ankylosing spondylitis, and a variety of other nonconnective tissue diseases. The only sera with elevated DNA-binding assays were from children with systemic lupus erythematosus. On the basis of these data, increased levels of antibodies to native DNA distinguished patients with active SLE from children with JRA.

Mucocutaneous lymph node syndrome: report of two cases complicated by gallbladder hydrops and diagnosed by ultrasound

Two patients with mucocutaneous lymph node syndrome are presented. During the course of their illnesses, they developed acute abdominal pain secondary to hydrops of the gallbladder. The diagnosis and management of each case was facilitated by ultrasonography.

A syndrome of childhood polyarteritis

In this report the clinical, laboratory, and histopathologic findings of nine children with polyarteritis are reviewed. All have had evidence of systemic involvement. Eight presented with fever, calf pain, erythematous painful nodules, and elevation of the acute-phase reactants. All were treated with prednisone at a dosage of 2 mg/kg/day. All of the children are alive but have had relapses at least once during the course of tapering the dosage of corticosteroids. Serious complications of disease have included myocardial infarction, hypertension, and impaired renal function.

Clinical patterns of chronic iridocyclitis in children with juvenile rheumatoid arthritis

In the present study we have reconfirmed an earlier observation of the association of iridocyclitis with limited joint involvement in children with JRA. Children who develop iridocyclitis are predominantly girls whose sera are positive for antinuclear antibodies. Iridocyclitis was found to be asymptomatic at onset. Only periodic slit lamp examinations will detect the majority of cases. Iridocyclitis began a median of 2 years after onset of arthritis. Although most episodes occurred within 7 years after onset of arthritis, the risk of this development may never be absent in these children, even after they enter adulthood. In the present study, 16% of the afflicted children experienced either unilateral or bilateral blindness.

Scleroderma in children

Fifteen children with scleroderma have been presented. All had characteristic cutaneous abnormalities at onset and during the course of disease. All were girls. All had visceral involvement, primarily of the gastrointestinal tract, heart, and lungs. The presence of visceral disease might have been missed without specific and extensive diagnostic procedures, including gastrointestinal barium studies, esophageal motility, pulmonary function and carbon monoxide diffusing capacity, and plethysmography. Raynaud's phenomenon was frequent and accompanied by evidence of occlusive vascular disease. Contractures around joints were readily evident and arthralgias were common, but evidence of objective arthritis was absent. Sixty percent of the patients in this series had ANA. Overlap syndromes with myositis and SLE were present in 7 patients. Three of 15 children died 6-10 years after onset of disease.

Dermatomyositis in the pediatric patient

Forty-one children with dermatomyositis who were treated with corticosteroids and who have been followed over a period of 15 years have been presented. Progressive proximal muscle weakness was seen in all and 60% had muscle pain. The skin rash considered classic for dermatomyositis was seen in 33 children at the time of diagnosis. Elevation of serum muscle enzymes, electromyographic abnormalities, and muscle biopsy evidence of acute myositis were of confirmatory diagnostic value. The course of the disease in this study group has reconfirmed the efficacy of adrenal corticosteroid treatment in conjunction with an individualized physical therapy program and consistent followup. Prognosis for life and minimal functional disability has been good. There have been 3 deaths recorded in this series, only one of which was certain in its relationship to dermatomyositis.

Serologic studies in juvenile rheumatoid arthritis: a review

Careful study of inflammatory and immunologic parameters in JRA and other connective tissue diseases of childhood has contributed to our current understanding of these diseases. Examination of serum for acute phase reactants, and antibodies to immunoglobulin antigens and nuclear antigens, combined with radiologic evaluation of symptomatic joints and, when indicated, examination of joint fluid or synovial membrane, may confirm the diagnosis of JRA. Changes in inflammatory indicators can be used as an index of adequacy of treatment. An ANA positivity in the child with pauciarticular arthritis should always prompt frequent slit-lamp examinations for asymptomatic iridocyclitis. The role played by auto-antibodies in the pathogenesis of JRA is unknown, as is the possible effect of proteins like CRP on the regulation of the inflammatory process in these children.

Pathogenic implications of age of onset in juvenile rheumatoid arthritis

An analysis of age of onset in juvenile rheumatoid arthritis was performed in the last 300 children seen in our clinic. There was a peak age of onset in girls at 1 to 3 years. Distribution of age of onset in boys was bimodal with the first peak at 2 years of age and the second at 9 years. There was no accentuation of frequency in either sex in the 10- to 14-year age group. The distribution of age of onset was bimodal in both monarticular and polyarticular onset of disease, but no particular modal age of onset was seen with systemic onset of disease. It is possible that these data reflect that JRA is not a homogenous disease, or that there are age-sex related differences in host susceptibility or pathogenic agents.

Abnormalities in the distribution of serum immunoglobulin concentrations in juvenile rheumatoid arthritis

Concentrations of serum IgG. IgA, and IgM were determined in 200 patients with juvenile rheumatoid arthritis. The relative frequency distribution of IgG and IgM approached that of a log-normal curve; however, there was marked skewing of the distribution of the serum concentrations of IgA. The prevalence of selective IgA deficiency was 4%. In order to permit further intragroup comparisons, the serum immunoglobulin concentrations were standardized by comparison to a sex-age matched control group. By this process it was found that there was concordance of the serum levels of IgG with IgA, and IgG with IgM. The standardized concentrations of IgA and IgM were less in females than males. The aberration in distribution of serum IgA concentrations found in this study, and the relative inability of females to respond to their disease by increasing specific serum immunoglobulin levels, add further data supporting the concept of immunodeficiency in the pathogenesis of juvenile rheumatoid arthritis.