## Facts

- Linda L. Sisco, a college-educated psychological assistant, developed persistent symptoms beginning in 1983 after a lymph gland infection with mononucleosis-like features.
- She experienced extreme fatigue, severe headaches, generalized muscle pain, and nausea, resulting in termination from her job in January 1984 and inability to sustain full-time work after February 1985.
- From 1985 to 1989, she was evaluated by more than fifteen physicians; many could not identify a physical cause for the severity of her symptoms, and some suggested psychological explanations.
- In 1989, the Mayo Clinic diagnosed her with tension myalgia and chronic fatigue syndrome (CFS) after extensive review and exclusion of other causes.
- A Mayo Clinic treating physician opined that Sisco was totally disabled because she could not sustain even sedentary activity (including sitting) for more than short periods without rest, and supported the diagnosis with contemporaneous medical literature.
- The Administrative Law Judge (ALJ) denied Social Security disability benefits, concluding CFS was not a medically determinable impairment because it lacked confirmation by medically acceptable clinical and laboratory diagnostic techniques, and treated her limitations as largely subjective.

## Issues

1. Whether substantial evidence supported the agency’s finding that Sisco’s CFS was not a medically determinable impairment under Social Security standards.
2. Whether the ALJ permissibly rejected the Mayo Clinic diagnosis and treating physician opinion because the condition lacked definitive laboratory testing.
3. Whether the ALJ properly evaluated Sisco’s symptom testimony given the clinical nature of CFS.

## Decision

- The Tenth Circuit reversed the district court’s affirmance of the benefits denial.
- The court held the agency decision was not supported by substantial evidence.
- The court ruled that CFS, when properly diagnosed using accepted medical standards, may qualify as a medically determinable impairment.
- The case was remanded for further proceedings consistent with the court’s analysis.

## Legal Principles

- An impairment may be medically determinable even when diagnosis rests primarily on clinical judgment, longitudinal observation, symptom patterns, and exclusion of other causes, where accepted medical criteria exist.
- An ALJ may not impose a requirement of traditional laboratory confirmation for conditions that are not readily susceptible to definitive objective testing.
- Treating and specialist opinions supported by a thorough clinical record and accepted medical sources may not be discounted merely because they rely on clinical evaluation and medical literature rather than definitive lab findings.
- Symptom testimony characteristic of an accepted medical condition may not be rejected solely due to lack of full objective corroboration, particularly where the condition itself commonly lacks classic laboratory markers.
- Substantial-evidence review requires considering the record as a whole; a denial cannot stand when the longitudinal medical evidence and supported functional limitations contradict the stated basis for rejecting impairment and disability.

## Conclusion

The Tenth Circuit concluded that the ALJ’s refusal to recognize clinically diagnosed CFS as a medically determinable impairment, and the related rejection of supported treating-source limitations and symptom evidence, lacked substantial evidentiary support; the court reversed and remanded for further proceedings.


Sisco v. U.S. Dep’t of Health & Hum. Servs., 10 F.3d 739 (10th Cir. 1993)