Structured Symptom Assessment to Identify Patients With Small Fiber or Autonomic Neuropathy in Fibromyalgia

Fibromyalgia (FM) is a complex chronic pain disorder characterized by widespread musculoskeletal pain and symptoms suggesting autonomic dysfunction. Small fiber neuropathy (SFN) has been described in a subgroup of patients. We aimed to explore the value of structured symptom assessment to identify patients with SFN or autonomic neuropathy.

Forty-six female FM patients were assessed in a cross-sectional study including clinical examinations, validated questionnaires (modified neuropathic pain symptom inventory (m-NPSI), PainDETECT and the composite autonomic symptom score (COMPASS 31)) and diagnostic tests (intraepidermal nerve fiber density (IENFD), quantitative sensory testing (QST) and quantitative sudomotor axon reflex test (QSART)). m-NPSI > 58, PainDETECT > 18, and COMPASS 31 > 16 were defined as suggestive of neuropathic pain and dysautonomia, respectively. SFN was defined as negative findings (hypoalgesia and reduced thermal sensation) and an abnormal diagnostic test (IENFD, thermal detection thresholds or QSART). Cardiovascular autonomic neuropathy (CAN) was defined as two abnormal cardiovascular reflex tests. Symptom scores were compared with patient controls and patients with an established diagnosis of neuropathy.

Among FM patients, one had SFN, while two had definite CAN. Thirty-two, 20, and 43 of the FM patients had NPSI, PainDETECT, and COMPASS 31 scores suggesting neuropathy/dysautonomia. NPSI was higher in FM than in neuropathy patients. Increased mechanical pain sensitivity (15/46) and paradoxical heat sensation (23/46) were frequent QST findings in the FM group.

SFN or autonomic neuropathy was infrequent in FM patients and not related to symptom scores, which were higher than those for patients with neuropathy.