Differential Diagnosis
- Single most likely diagnosis
- D) Tay-Sachs disease: This is the most likely diagnosis due to the patient's symptoms, including a decline in motor skills (needing help sitting upright after previously being able to sit independently), startling easily to noises, and the presence of a cherry-red spot on the macula (indicated by pallor of the retinal background and a reddish macula). The family history of a cousin dying from a seizure disorder during infancy and the parents being second cousins also supports this diagnosis, as Tay-Sachs disease is an autosomal recessive disorder.
- Other Likely diagnoses
- C) Mucopolysaccharidosis I: Although less likely, this diagnosis could be considered due to the patient's developmental decline and the presence of a cherry-red spot. However, mucopolysaccharidosis I typically presents with more systemic symptoms, such as coarse facial features and hepatosplenomegaly, which are not mentioned in the case.
- Do Not Miss
- A) Cytomegalovirus encephalopathy: Although less likely, congenital cytomegalovirus infection can cause neurological symptoms, including developmental delay and seizures. It is essential to consider this diagnosis due to its potential for severe consequences if left untreated.
- B) HIV encephalopathy: Similarly, HIV encephalopathy can cause neurological symptoms, including developmental delay and decline. Given the potential severity of HIV infection, it is crucial to rule out this diagnosis.
- Rare diagnoses
- E) Tuberous sclerosis: This diagnosis is less likely, as tuberous sclerosis typically presents with a range of symptoms, including skin lesions, renal angiomyolipomas, and cardiac rhabdomyomas, which are not mentioned in the case. However, it can cause neurological symptoms, including seizures and developmental delay, so it should be considered in the differential diagnosis.