Validation of diagnostic codes for Charcot–Marie–Tooth disease in the Danish National Patient Registry

Figures & data

Figure 1 Flowchart of the validation process

Notes: ^aSelection in the DNPR: at least one primary diagnosis given at a department of neurology, neurophysiology, clinical genetics, or pediatrics during 1977–2012; ^brandom sample: 20 cases for every 5 years from 1977 to 2012.
Abbreviations: CMT, Charcot-Marie-Tooth disease; CDR, Central Denmark Region; DNPR, Danish National Patient Registry; N, number of cases.

Table 1 Criteria for validationa and distribution of fulfilled criteria among the 87 cases without genetically confirmed diagnosis

Criteria for CMT validation	Fulfilled criteria
	N (% of group)
	CMT (N=76)	Non-CMT (N=11)	All cases (N=87)
1. Neurophysiological evaluation or nerve biopsy consistent with CMT	59 (77.6)	3 (27.3)	62 (71.2)
2. Muscle weakness of the lower limbs	66 (86.8)	1 (9.1)	67 (77.0)
3. Reduced or loss of tendon reflexes of the lower limbs	66 (86.8)	6 (54.5)	72 (82.8)
4. Muscle atrophy	57 (75.0)	3 (27.3)	60 (69.0)
5. Foot deformities	57 (75.0)	2 (18.2)	59 (67.8)
6. Family history of CMT	47 (61.8)	2 (18.2)	49 (56.3)
7. Disease onset before age of 35 years	57 (75.0)	6 (54.5)	63 (72.4)

Note:

a In order to validate a case as CMT, at least four out of the seven criteria had to be fulfilled, and at least one of the fulfilled criteria had to be criteria number 1, 2, or 3.

Abbreviations: CMT, Charcot-Marie-Tooth disease; N, number of cases.

Table 2 Validity of the Charcot-Marie-Tooth diagnosis in the DNPR

Category	Total no. of cases	No. of CMT cases	No. of non-CMT cases	PPV (%)	95% CI
All	96	85	11	88.5	80.4–94.1
Year of diagnosis
1977–1999	43	37	6	86.0	72.1–94.7
2000–2012	53	48	5	90.6	79.3–96.9
Age at diagnosis (years)
0–29	28	24	4	85.7	67.3–96.0
30–49	32	31	1	96.9	83.8–99.9
≥50	36	30	6	83.3	67.2–93.6
Gender
Males	33	27	6	81.8	64.5–93.0
Females	63	58	5	92.1	82.4–97.4

Abbreviations: DNPR, Danish National Patient Registry; CMT, Charcot-Marie-Tooth disease; PPV, positive predictive value; CI, confidence interval.