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Three Part Question

In [a male child with speech delay who walks prior to 18 months old], does [requesting serum creatine kinase] help [diagnose Duchenne muscular dystrophy with reasonable efficiency]?

Clinical Scenario

Jack is a 2.5 year old boy. He has been referred for developmental assessment by his health visitor. His community paediatrician diagnoses speech and language delay. His mother reports he first sat independently at 9 months and walked at 17 months.

Search Strategy

PubMed August 2006
"Duchenne muscular dystrophy," "speech delay", combined with "screening" and "language". Sixteen references were found in total.

Search Outcome

OMIM database and specific journals: The titles and the abstracts were reviewed. Eleven studies were relevant; seven articles were selected as directly related to the question.

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Parsons et al, 2004,	22 boys diagnosed in newborn screening programme 1990-1998	Cohort study 1b	Previously proposed strategies for earlier diagnosis would have limited effectiveness in the newborn screening group	Not walking at 18 months: 22%. Speech delay at 24 months: 56%. Awkward gait at <4 years:94%	Analysed suggested screening criteria Used Griffith scales, developmental milestones, case reviews and parental report
Mohammed et al, 2000,	21 boys attending a regional paediatric neuromuscular clinic 1995-1998	Retrospective case note review 4	Diagnosis remains delayed. Previous analysis in 1995 from the same clinic showed mean age of diagnosis of 4.5 years in a total of 51 boys	Mean age of diagnosis:3.2 years. When neonatal diagnosis excluded, mean age rose to 4.5 years 72% had been seen by another hospital or community doctor prior to the diagnosis being considered	Suggests clinical criteria that should justify a CK measurement
Cotton et al, 1998,	1224 children with muscular dystrophy	Meta-analysis 2a	Looked specifically at verbal and performance IQ Results suggested no significant difference overall but considered the possibility of subgroups within the muscular dystrophy population with lower than expected language scores	Impairments reported in language scores Population mean IQ in DMD 1 SD lower than in normal population	Highlighted the influence that motor co-ordination may have on IQ tests
Smith et al, 1989,	19,930 participants	Cohort study 1b	Picked up 2 affected boys	1.7% not walking at 18 months. CK checked in 61%	Concluded that population based screening had unacceptably low yield
Dorling et al, 2001,	Analysis of a case of a boy with delayed walking	Case study 5	Calculated the risk of a boy not walking at 18 months having DMD as 1:228		Comment: Gives a cost benefit analysis for checking CK
Essex et al, 2001,	3 patients	Case series 4	In the authors opinion a late diagnosis of DMD is especially likely in boys with a considerable learning difficulty who present with global delay	In each case the delay to diagnosis was felt to be unacceptable All 3 children had significant language delay	Small case series highlighting reasons for late diagnosis

Comment(s)

The early diagnosis of Duchenne muscular dystrophy (DMD) in the male child with developmental delay is a frequent concern in community paediatric practice. Many criteria have been suggested as "triggers" to screen for the condition. Most focus on delayed motor milestones as this has been clearly shown to be symptomatic of DMD. Other criteria have included speech delay. These parameters appear to be robust when followed prospectively in a cohort of affected boys in the Newborn Screening Study in Wales. Speech problems in boys with DMD have been extensively researched as the mechanism remains unclear. The Welsh cohort demonstrated that 71% of affected boys failed one or both of the speech and language developmental milestones studied (single words at >13.7 months and meaningful sentences at >29 months). The authors point out that there was no clear link between late walking and delayed language development in this group (Parsons). Speech and language delay (SLD) is common and DMD is relatively uncommon. Assuming an incidence of DMD of 1 in 3000 male births (Brown) and a prevalence of SLD of 61% in DMD 8 versus 6% in the general preschool population (USPSTF, Law) allows construction of a two-way contingency table (Deeks). The positive predictive value of SLD as a screening tool for DMD is unsurprisingly low (0.34%) and the negative predictive value unsurprisingly high (99.99%) largely because of the low prevalence of DMD. Approximately 300 children with SLD would have to be tested to identify one child with DMD. It is important to note that a number of boys with DMD will have normal speech development and up to 70% walk at 18 months. At presentation boys may report more non-specific symptoms such as cramps, leg pains or clumsy gait; it is worth specific, detailed questioning of parents of boys with speech delay to elucidate these subtle symptoms.

Editor Comment

CK, creatine kinase; DMD, Duchenne muscular dystrophy.

Clinical Bottom Line

Speech and language delay (SLD) in Duchenne muscular dystrophy (DMD) is ten times more common than in the general population (60%). (Grade C) Approximately 300 boys with SLD would need creatine kinase (CK) tests to diagnose one with DMD. (Grade C) Any subtle signs or symptoms of locomotor delay should prompt serum CK testing. (Grade D)

References

1. Parsons EP, Clarke AJ, Bradley DM. Developmental progress in Duchenne muscular dystrophy: lessons for earlier detection. Eur J Paediatr Neurol 2004;8:145–53.
2. Mohamed K, Appleton R. Nicolaides P. Delayed diagnosis of Duchenne muscular dystrophy. Eur J Paediatr Neurol 2000;4:219–23.
3. Cotton S, Crowe SF. Voudouris N. et al. Neuropsychological profile of Duchenne muscular dystrophy. Child Neuropsychol 1998;2:14.
4. Smith RA, Rogers M, Bradley DM, et al. Screening for Duchenne muscular dystrophy. Arch Dis Child 1989;64:1017–21.
5. Dorling J, Salt A. Assessing developmental delay. BMJ 2001;323(7305):148-9.
6. Essex C. Roper H. Lesson of the week: late diagnosis of Duchenne muscular dystrophy. BMJ 2001;323(7303):37-8.
7. Brown JK. Minns RA. Disorders of the central nervous system. In: Campbell AGM, McIntosh N, eds. Forfar and Arneil's textbook of pediatrics. Edinburgh: Churchill Livingstone, 2006:641-842.
8. Smith RA, Sibert JR, Wallace SJ, et al. Early diagnosis and secondary prevention of Duchenne muscular dystrophy. Arch Dis Child 1989;64:787–90.
9. US Preventative Services Task Force. Screening for speech and language delay in preschool children: recommendation statement. Am Fam Physician 2006;73(9):1605-10.
10. Law J, Boyle J, Harris F, et al. Screening for speech and language delay: a systematic review of the literature. Health Technol Assess 1998;2(9):1-184.
11. Deeks JJ, Altman DG. Diagnostic tests 4: likelihood ratios. BMJ 2004;329:168–9.