A 12-year-old boy comes to the clinic for a physical examination prior to attending camp. He is generally healthy. He has a reading disability and has been diagnosed with attention-deficit disorder, for which he takes medication. On physical examination, his height is 167 cm (>97th percentile), weight is 45 kg (75th percentile), and head circumference is 54 cm (50th percentile). The arm span-to-height ratio is greater than the 97th percentile, and the upper-to-lower segment ratio is less than the 10th percentile. He has five café au lait macules measuring 5 mm or more. He is prepubertal. The remainder of the physical examination findings are unremarkable. He seems shy and does not establish eye contact with you during the examination.
Of the following, the MOST appropriate next step toward providing comprehensive care for this boy is to
A. arrange for echocardiography
B. order magnetic resonance imaging of the head
C. refer him to an ophthalmologist
D. request renal ultrasonography
E. send blood for chromosome analysis
Correct option is 'E'
Explanation:
The boy described in the vignette has tall stature, long arms and legs, difficulty with reading, and appears to be socially uncomfortable. Although this combination of features is not pathognomonic for a specific diagnosis, it is consistent with a possible diagnosis of Klinefelter syndrome (KS).
KS is the most common sex chromosome abnormality and the leading cause of male infertility. It is estimated to occur in 1 in 600 male births, and most individuals are not diagnosed. The karyotype most often associated with KS is 47,XXY, but more than one extra X chromosome may be present. The diagnosis can be made with chromosome analysis.
Infants who have KS typically have normal length, weight, and head circumference, but as the children approach school age, height velocity increases such that affected boys frequently are tall compared with their classmates. As teenagers, the boys typically are at the 80th percentile or above for height, and they have relatively long arms and legs. Prepubertal children who have KS usually do not have dysmorphisms.
From a developmental standpoint, children who have KS tend to have mildly delayed motor and language development. Additionally, they may display mildly low muscle tone, and they often have a calm demeanor.
Hypotonia sometimes results in delayed acquisition of motor skills. Additionally, language development may be mildly delayed. It is important to note, however, that many affected boys have completely normal development.
Typically, boys who have KS have normal intellectual ability, although it is slightly decreased from that of the general population. Verbal and reading skills are the areas of greatest academic weakness, and a significant percentage of affected boys may have reading disabilities (>50% in at least one study).
The boys tend to be shy and sedentary and often suffer from poor self-esteem. They frequently display immature behaviors compared with their same-age peers. They typically do not excel at sports. This combination of features may result in depression and, occasionally, aggressive behaviors.
Boys who have KS generally have normal findings on physical examination until puberty, when the testes fail to enlarge as expected. Approximately 15% develop gynecomastia, and there may be reduced facial, axillary, and pubic hair compared with the average.
The management of individuals who have KS includes evaluation for testosterone deficiency, with the initiation of testosterone replacement therapy in mid- to late adolescence. Baseline testosterone, follicle-stimulating hormone, and leuteinizing hormone levels should be measured at 12 to 13 years of age or when the diagnosis initially is made (if later).
Individuals who have KS are at increased risk for breast cancer in adulthood. Recent reports suggest that this risk is approximately 3%. Additionally, there is evidence that affected individuals are at increased risk for primary mediastinal germ cell tumors, although the lifetime risk is approximately 1%.
The differential diagnosis of patients who present with features of KS includes Marfan syndrome. Marfan syndrome is characterized by multiple skeletal anomalies, including dolichocephaly and arachnodactyly, none of which are present in the boy described in the vignette. Should Marfan syndrome be a strong consideration, echocardiography and ophthalmology evaluations are warranted.
The boy described in the vignette has five café au lait macules. The finding of six or more café au lait macules measuring at least 5 mm in a prepubertal individual should alert the examiner to the possible diagnosis of neurofibromatosis (NF), most commonly type 1. If an individual meets the diagnostic criteria for NF-1, head imaging (most commonly head magnetic resonance imaging) may be recommended. Because the patient described in the
vignette has no symptoms or signs of renal disease, and renal anomalies are not a feature of KS, there is no indication for renal ultrasonography.
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