Simian Crease: Clinical Implications and Evaluation
A simian crease (single transverse palmar crease) warrants systematic evaluation for chromosomal abnormalities—particularly Down syndrome—and other genetic syndromes, though it occurs in approximately 14.6% of normal individuals with significant ethnic variation.
Clinical Significance and Associations
The simian crease is most strongly associated with Down syndrome (trisomy 21), where it serves as a useful diagnostic marker when combined with other minor physical anomalies. 1 However, clinicians must recognize that this finding alone is not pathognomonic for any condition.
Key Associations:
- Down syndrome: The simian crease is one of the characteristic morphological features, though not universally present 1, 2
- Other chromosomal anomalies: Various genetic disorders demonstrate increased incidence 3
- Childhood malignancies: Unusual palmar creases (simian or Sydney type) occur in >50% of children with malignant neoplasia, particularly acute lymphocytic leukemia and embryonic tumors 4
- Normal variant: Present in 14.6% of healthy Nepalese children, with striking ethnic variation (71.2% in Lama population) 5
Diagnostic Algorithm
Initial Clinical Assessment
When a simian crease is identified, perform a systematic evaluation for Down syndrome using the following high-yield physical findings:
- Epicanthus and telecanthus together: Sensitivity 0.945 for Down syndrome 1
- Clinodactyly (curved fifth finger) and high-arched palate together: Sensitivity 0.945 with negative predictive value 0.979 1
- Additional features: Big sandal gap (increased space between first and second toes), brachycephaly, flat facial profile 1
Critical Pitfall to Avoid
Do not rely on simian crease alone as a diagnostic criterion—it is not specific for Down syndrome and requires correlation with other minor physical anomalies. 1 The presence of epicanthus, telecanthus, high-arched palate, and curved fifth finger serve as differentiating anomalies with much higher diagnostic value.
Recommended Evaluation Strategy
For Bilateral Simian Creases:
- Karyotyping is indicated when bilateral simian creases are present with other dysmorphic features, as bilateral occurrence is rare in healthy individuals 4
- Evaluate for Marfan syndrome and related connective tissue disorders if the patient is tall and lanky, though simian crease is not a primary feature 6
For Unilateral Simian Crease:
- Document ethnic background: Certain populations (particularly Lama ethnicity) have markedly elevated baseline incidence 5
- Perform targeted physical examination for Down syndrome features listed above 1
- Consider family history: Unusual palmar creases show familial clustering, with significantly higher frequencies in parents and siblings of affected children 4
When to Pursue Genetic Testing
Proceed with karyotyping when:
- Bilateral simian creases are present 4
- Simian crease occurs with ≥2 of the following: epicanthus, telecanthus, high-arched palate, clinodactyly 1
- Associated developmental delay or intellectual disability is present 1
- Family history of chromosomal abnormalities exists 4
- Patient presents with childhood malignancy (particularly ALL or embryonic tumors in early childhood) 4
Special Considerations
Parental and sibling evaluation may be warranted, as unusual palmar creases demonstrate familial patterns with striking incidence in younger siblings of patients with childhood neoplasia 4. This suggests a possible common host factor associated with cellular growth, differentiation, and cell-mediated immune response 4.
The axial triradius angle should be measured in patients with simian crease, as it differs significantly between those with and without the crease across ethnic groups 5. This provides additional anthropometric data for comprehensive evaluation.
Outcome Prioritization
The primary clinical imperative is early identification of Down syndrome to enable:
- Timely cardiac evaluation (40-50% have congenital heart defects)
- Appropriate developmental interventions
- Family counseling and support
- Screening for associated conditions (thyroid dysfunction, leukemia, hearing/vision problems)
Secondary consideration involves recognizing the association with childhood malignancies, particularly when unusual creases appear bilaterally, to ensure appropriate surveillance in high-risk patients 4.