What could be causing bilateral arm cramps in a patient with a history of cystic teratoma?

Bilateral Arm Cramps: Evaluation and Management

In a patient with a history of cystic teratoma presenting with bilateral arm cramps, the most critical consideration is anti-NMDA receptor encephalitis, which occurs in 20-50% of female patients with ovarian teratomas and characteristically presents with movement disorders including involuntary muscle movements that could manifest as cramping sensations. 1, 2

Primary Diagnostic Consideration: Anti-NMDA Receptor Encephalitis

Clinical Recognition

• Movement disorders are characteristic of NMDAR encephalitis and can include various involuntary movements such as lip smacking, choreoathetosis, and picking behaviors that patients may describe as "cramping" or abnormal muscle sensations 1, 3
• The median age of presentation is 25 years with a female-to-male ratio of 2:1 1, 2
• Additional features to assess include: psychiatric symptoms (new-onset psychosis, behavioral disturbances), seizures, aphasia, and autonomic instability 3

Immediate Diagnostic Workup

• Send serum and CSF for anti-NMDA receptor antibodies immediately without waiting for results before initiating treatment 1
• Perform transvaginal or transabdominal pelvic ultrasound to screen for ovarian teratoma 1, 2
• If ultrasound is equivocal, obtain pelvic MRI 2
• Exclude infectious encephalitis with multiplex PCR for HSV and obtain brain MRI 1

Treatment Algorithm

• Initiate immunotherapy immediately once infection is excluded, using pulse-dose methylprednisolone and either IVIG or plasma exchange, without waiting for antibody confirmation 1
• Surgical removal of any identified ovarian teratoma is critical and should be performed as soon as the patient is medically stable 1, 2
• If no response to first-line treatment occurs within 2-4 weeks, rituximab is the preferred second-line therapy 1

Alternative Considerations if NMDAR Encephalitis is Excluded

Neurovascular Compression Syndromes

If the cramping is truly localized to the arms with reproducible positional triggers, consider thoracic outlet syndrome (TOS):

• Neurological TOS presents with chronic arm paresthesia, numbness, or weakness affecting the upper extremities bilaterally if anatomic variants are present 3
• Symptoms worsen with repetitive upper-extremity movement or extreme shoulder abduction 3
• CT or MRI in neutral and stressed positions can identify anatomic narrowing of the costoclavicular or interscalene triangles 3

Metabolic and Electrolyte Disturbances

• Assess for hypocalcemia, hypomagnesemia, and hypokalemia which commonly cause muscle cramping
• Check thyroid function and vitamin D levels
• Review medications that may precipitate cramping (diuretics, statins)

Critical Clinical Pitfalls

The most dangerous error would be dismissing bilateral arm symptoms as simple muscle cramps in a patient with known teratoma history without screening for NMDAR encephalitis, as delayed diagnosis significantly worsens neurological outcomes 1, 3

• Tumor screening should be performed annually for several years if NMDAR encephalitis is diagnosed, particularly if treatment response is poor or relapses occur 2
• Even if initial teratoma screening is negative, repeat imaging may be necessary as tumors can be occult initially 2
• The presence of a known cystic teratoma increases the pre-test probability of NMDAR encephalitis substantially 1, 2