F39. Parsonage from a power tool: An unusual presentation of neuralgic amyotrophy in a 78 year old woman after using a chainsaw

Abstract

Introduction A 78 year old Caucasian female presented for an electrodiagnostic (EDX) evaluation for right hand weakness and atrophy. Symptoms began 3 months prior one day after she was working with a chainsaw in the backyard and experienced severe right scapular pain followed by a monophasic course of progressively worsening weakness, inability to grip things such as a pen or coffee cup, and numbness and tingling into digits 1–3. Exam showed right sided prominent atrophy of the first dorsal interosseous (FDI) and thenar eminence, 4/5 strength in shoulder abduction and elbow flexion/extension, 3/5 strength in finger flexion and abduction, a positive okay sign, diminished sensation throughout the right upper limb. She also has weakness of the serratus anterior with mild medial winging of the right scapula during anteflexion. Myelogram and computed tomography showed no significant neural compression to explain patient’s symptoms, specifically no C8 compression. Methods The patient underwent EDX testing and a neuromuscular ultrasound. Results Nerve conduction studies showed prolonged distal onset latency and reduced amplitude of the right median motor nerve and no response in the right ulnar motor nerve, but were otherwise normal. Needle evaluation of the right FDI muscle showed reduced insertional activity with no recruitment of motor units, and the right pronator quadratus muscle showed reduced recruitment. Neuromuscular ultrasound of the right brachial plexus showed some increased hypoechogenicity and possible increased caliber compared to the left. The right forearm musculature including the pronator quadratus and FDI demonstrated increased hyperechogenicity and atrophy consistent with chronic denervation. Patient was diagnosed with a distal predominant neuralgic amyotrophy (NA) variant. Conclusion Neuralgic amyotrophy (NA), also known as Parsonage-Turner Syndrome, exhibits a high degree of phenotypic variability with only two-thirds of patients presenting with the classic phenotype with its predilection for the superior trunk of the brachial plexus. In this case, the patient met 5/5 of the clinical criteria for NA as defined by Van Alfen and neuromuscular ultrasound was helpful in further confirming the diagnosis. NA should be considered in patients even if they do not fit the classic phenotype of predominately proximal arm weakness and ultrasound of the plexus and affected muscles can be a helpful adjunctive diagnostic tool is such cases which do not “fit the textbook.”