Deep Tendon Reflexes in a 70-Year-Old with Tarlov Cyst
In a 70-year-old patient with a Tarlov cyst, upper extremity deep tendon reflexes (biceps, brachioradialis, triceps) should be normal (2+ bilaterally), while lower extremity reflexes may be diminished or absent depending on which sacral nerve roots (S2-S4) are affected by the cyst.
Understanding the Neuroanatomy
Tarlov cysts are perineural cysts that occur at the sacral nerve roots, most commonly affecting S2-S4 levels 1. These cysts can cause:
- Sacral nerve root compression leading to dysfunction of the lower sacral segments
- Preservation of lumbar nerve roots (L2-L4), which mediate the patellar reflex
- No involvement of upper extremity innervation (C5-T1), leaving upper extremity reflexes intact
Expected Reflex Pattern
Upper Extremity DTRs (Should be Normal)
- Biceps reflex (C5-C6): 2+ bilaterally
- Brachioradialis reflex (C5-C6): 2+ bilaterally
- Triceps reflex (C7-C8): 2+ bilaterally
These remain unaffected because Tarlov cysts are anatomically distant from cervical nerve roots.
Lower Extremity DTRs (May be Abnormal)
Patellar reflex (L2-L4): Typically normal (2+) because lumbar roots are above the typical Tarlov cyst location 2.
Ankle reflex (S1-S2): Often diminished (1+) or absent (0) because S1-S2 roots are commonly affected by sacral Tarlov cysts 1.
Clinical Correlation
The lower sacral nerve roots (S2-S4) innervate the urinary and anal sphincters, and damage to these structures can result in bowel/bladder dysfunction 1. A key clinical finding is that patients with symptomatic Tarlov cysts often present with sitting intolerance, perineal sensory changes, and sacral radicular pain 3, rather than primarily reflex changes.
Important Caveats
Age consideration: In a 70-year-old, diminished ankle reflexes may be age-related rather than pathological 4, 5. The diagnostic specificity of reflexes decreases with age (70-95% in younger patients, lower in elderly) 5.
Preserved reflexes don't exclude pathology: Up to 35% of patients with polyneuropathies have normal clinical DTRs 4. Similarly, normal reflexes do not exclude symptomatic Tarlov cysts if the clinical picture (sitting intolerance, perineal symptoms) is suggestive 3.
Asymmetry is a red flag: If reflexes are markedly asymmetric or if upper extremity reflexes are abnormal, consider alternative diagnoses such as cervical myelopathy or other central nervous system pathology 6.
Example of Normal Lower Extremity DTR Pattern
In a 70-year-old with an asymptomatic Tarlov cyst:
- Patellar (knee) reflex: 2+ bilaterally (normal)
- Ankle reflex: 1+ bilaterally (may be age-related diminution, not necessarily pathological)
This pattern reflects preserved lumbar root function with possible age-related or mild sacral involvement.