Differential Diagnosis for Diarrhea Followed by Neck Stiffness Without Fever

Single Most Likely Diagnosis

• Viral Gastroenteritis with Secondary Meningismus: This condition is likely due to the initial gastrointestinal symptoms (diarrhea) followed by neck stiffness, which could be a result of viral meningitis or aseptic meningitis, where the absence of fever does not rule out the condition, especially in the early stages.

Other Likely Diagnoses

• Food Poisoning with Neurological Complications: Certain types of food poisoning (e.g., from Staphylococcus aureus, Bacillus cereus) can cause gastrointestinal symptoms followed by neurological symptoms, including neck stiffness, due to toxins.
• Enteroviral Infection: Enteroviruses can cause a range of symptoms, including gastrointestinal distress and neurological manifestations like meningismus without fever, especially in children.
• Bacterial Gastroenteritis with Secondary Infection: Although less common, bacterial causes of gastroenteritis (like Salmonella, E. coli) could potentially lead to secondary infections or complications that might cause neck stiffness.

Do Not Miss Diagnoses

• Meningitis (Bacterial or Viral): Although the absence of fever makes bacterial meningitis less likely, it is crucial not to miss this diagnosis due to its high morbidity and mortality. Viral meningitis can also present without fever, especially in the early stages.
• Encephalitis: Inflammation of the brain, which can be caused by viruses or other pathogens, might present with gastrointestinal symptoms followed by neurological signs like neck stiffness.
• Subarachnoid Hemorrhage: A life-threatening condition that could present with sudden onset of severe headache and neck stiffness, though typically accompanied by other symptoms like severe headache.

Rare Diagnoses

• Guillain-Barré Syndrome: An autoimmune disorder that can follow a gastrointestinal infection, leading to ascending paralysis and potentially neck stiffness, though this is less common.
• Carcinoid Syndrome: In rare cases, carcinoid tumors can cause gastrointestinal symptoms and, through metastasis or other mechanisms, lead to neurological symptoms, including neck stiffness.
• Neurological Manifestations of Systemic Diseases: Certain systemic diseases (e.g., lupus, sarcoidosis) can have gastrointestinal and neurological manifestations, including diarrhea and neck stiffness, though these would be uncommon presentations.