Case Presentation: 40-year-old woman with history of pernicious anemia, fibromyalgia and depression presented with progressive fatigue and weakness with associated myalgias and bilateral hip and shoulder girdle pain. Outpatient evaluation initially attributed these symptoms to worsening depression and fibromyalgia and amitriptyline was prescribed. Unfortunately, symptoms progressed and baclofen was started with minimal relief. Over the course of the next two months, an extensive workup was performed. Blood work revealed an unremarkable CBC and CMP. SPEP, UPEP, CPK levels and thyroid function panel were normal. ANA, ANCA, anti-MuSK and AChR antibodies were negative. MRI of the brain and spine, EEG, EMG and lumbar puncture were all unrevealing. Interestingly, ESR and CRP were elevated at 70 and 2.37, respectively, and a paraneoplastic autoantibody profile was positive for anti-striated muscle antibodies, N-type calcium channel antibodies and neuronal voltage-gated potassium channel antibodies. Moreover, anti-glutamic acid decarboxylase (anti-GAD) antibodies were elevated at 465. On presentation, patient was afebrile and hemodynamically stable. Examination revealed diffuse tenderness to palpation along bilateral shoulder and hip girdles with decreased range of motion but no signs of synovitis. Marked weakness was observed in the proximal muscle groups of the upper and lower extremities bilaterally with intact sensation and deep tendon reflexes. Right temporal tenderness was elicited with normal ophthalmic exam. Initial blood work showed an elevated ESR and CRP. Right temporal artery biopsy showed no evidence of temporal arteritis. Rickettsial antibodies and all other infectious workup were negative. Clinical history and examination with positive autoantibodies was concerning for stiff person syndrome. High dose benzodiazepine was started, and IVIg and methylprednisolone were administered daily for five days. Pan-CT was negative for tumor. Pain began to gradually resolve and range of motion improved. Patient began to participate in physical and occupational therapy and was discharged to acute rehab.

Discussion: Weakness and musculoskeletal pain are commonly seen by the hospitalist. Often patients are overlooked due to their pre-existing conditions, such as fibromyalgia and depression. Stiff person syndrome (SPS) is a neurologic condition characterized by rigidity, stiffness and muscle spasms. SPS is believed to be caused by an autoimmune process as it is often associated with an autoimmune disorder, such as pernicious anemia, and anti-GAD antibodies are positive in approximately 60% of patients. Additionally, all patients with SPS should undergo a thorough cancer evaluation as there is a paraneoplastic subset. Benzodiazepines and baclofen are often successful for symptom relief. Immunosuppressive therapy with glucocorticoids and IVIg are used for extreme and/or refractory symptoms, as in our patient. Prognosis is variable and a gradual decline in function may occur.

Conclusions: It is important to keep a broad differential in mind when working with patients with muscle weakness and to not close the door on patients with comorbidities.