Extrapyramidal signs occurring after sympathetic block for complex regional pain syndrome responding to diphenhydramine: Two case reports.

Rationale: To present an unusual extrapyramidal motor response occurring after a sympathetic block in CRPS and its successful treatment with diphenhydramine.

Patient Concerns: Severe pain related to Complex Regional Pain Syndrome type 1 interfering with activities of daily living.

Diagnoses: Complex Regional Pain Syndrome type 1.

Interventions: We report a video case reports of two patients with a diagnosis of CRPS type-I. Both patients exhibited similar presentation of unusual extrapyramidal motor response of the affected limb following lumbar sympathetic block. Both patients were treated with intravenous diphenhydramine to abort the extrapyramidal motor response.

Outcomes: Both patients similarly responded to treatment with intravenous diphenhydramine with abrupt resolution of the motor response.

Lessons: Sympathetic blockade may interfere with the adaptive autonomic reflex circuits of the motor balance homeostasis in patients with complex regional pain syndrome. Disinhibition of extrapyramidal system may lead to immediate expression of extrapyramidal signs following the sympathetic block. Diphenhydramine, with its anti-histaminic and anticholinergic properties, may be effective in aborting such extrapyramidal signs, and should be considered as a treatment option in similar cases.