Final answer:
The main drawback of a paired stimulus assessment is its possible failure to detect subtle interaction issues in the sensory pathways, potentially leading to misdiagnosis if only gross deficits are considered. It is important to conduct a comprehensive review of sensory functions, as errors in perception during this assessment might point to more complex pathway defects.
Step-by-step explanation:
The con of a paired stimulus assessment such as in double simultaneous stimulation, which is used to assess the perception of laterality, may overlook complexities in the sensory pathways. For instance, if a deficit is observed in the patient's ability to sense stimuli on one side during the assessment, this could indicate potential damage to the contralateral posterior parietal lobe. While the assessment can effectively compare the major ascending tracts to uncover sensory discrimination issues, it may not detect intricate interactions between the tracts, as each pathway operates independently on either side of the spinal cord. Therefore, if no deficits are identified in other subtests focusing on specific pathways, the conclusion is typically that the impairment is located in the cortex, the region responsible for conscious perception.
The mental status exam, which includes paired stimulus assessment, further explores cortical functions through additional subtests such as stereognosis and graphesthesia. These are also localized primarily to the parietal cortex and can provide a more comprehensive view of a patient's sensory perception capabilities.
In summary, the main disadvantage of a paired stimulus assessment lies in its potential to miss subtle defects in the somatosensory system which could inform about errors in ascending projections, especially when the basic sensory stimuli appear to be normal. Recognizing pain as light touch or vice versa during the pairing of light touch and pain subtests might indicate such projection errors, highlighting the importance of a detailed examination when assessing somatosensory function.