Differential Diagnosis for the 6-Month-Old Girl
Single Most Likely Diagnosis
- Developmental Delay: The infant's inability to sit without support, failure to pull to stand, and absence of crawling at 6 months suggest a gross motor delay. The lack of babbling indicates a potential speech delay. However, her ability to transfer toys and respond to her name suggests some preservation of fine motor and cognitive skills.
Other Likely Diagnoses
- Muscular Dystrophy: The absence of Moro and grasp reflexes, along with gross motor delays, could be indicative of a muscular dystrophy. However, this would typically be accompanied by other signs such as hypotonia or muscle weakness.
- Cerebral Palsy: The infant's gross motor delays, particularly the inability to sit without support and the presence of a positive Babinski sign (big toes turning up with firm stroking of the soles), could suggest cerebral palsy. However, a definitive diagnosis typically requires more pronounced and persistent signs.
- Genetic Disorders: Given the family history of speech delay in the 2-year-old brother, there could be a genetic component to the infant's developmental delays. Conditions such as fragile X syndrome or other genetic disorders affecting development should be considered.
Do Not Miss Diagnoses
- Spinal Muscular Atrophy (SMA): This is a severe and progressive condition that affects muscle strength and movement. Early signs can include weakness, hypotonia, and developmental delays. SMA is a critical diagnosis not to miss due to the availability of disease-modifying treatments that can significantly improve outcomes if started early.
- Metabolic Disorders: Certain metabolic disorders, such as those affecting amino acid or organic acid metabolism, can present with developmental delays. These conditions often require prompt diagnosis and treatment to prevent long-term damage.
Rare Diagnoses
- Rett Syndrome: A rare genetic disorder that affects brain development, leading to severe mental and physical disability. It is characterized by a period of normal development followed by regression, which does not seem to fit this infant's presentation at this stage.
- Prader-Willi Syndrome: A rare genetic disorder that can cause a range of physical, mental, and behavioral problems. Early signs may include hypotonia and feeding difficulties, which are not prominently featured in this case.