Diagnosis: Chronic Inflammatory Demyelinating Polyneuropathy (CIDP)
The most likely diagnosis is chronic inflammatory demyelinating polyneuropathy (CIDP), given the 4-month progressive course, symmetric ascending weakness affecting both proximal and distal muscles, absent reflexes, and lack of acute findings on brain MRI. 1, 2
Key Distinguishing Features Supporting CIDP
The clinical presentation strongly favors CIDP over the other differential diagnoses based on the following:
Timeline is critical: The 4-month progressive course with symptoms "off and on" definitively excludes Guillain-Barré syndrome (GBS), which progresses over days to 4 weeks (typically <2 weeks). 1 CIDP progresses over more than 2 months, which matches this patient's presentation. 2
Pattern of weakness: The combination of 3/5 upper extremity and 2/5 lower extremity strength with absent reflexes throughout indicates a symmetric, motor-predominant polyradiculoneuropathy affecting both proximal and distal muscles—the hallmark of CIDP. 3, 4 This symmetric pattern with areflexia is characteristic of the classical CIDP subtype. 3
Age and demographics: CIDP typically affects younger to middle-aged adults and can present in patients in their 20s, unlike GBS which has increasing incidence with age. 4
Why Not the Other Diagnoses?
Guillain-Barré syndrome is excluded because GBS reaches maximum disability within 2 weeks in most cases, with rapid progression over days. 1 This patient has had symptoms for 4 months with gradual worsening over 2 weeks—far too prolonged for GBS. 1
Multiple sclerosis is unlikely because the brain MRI showed no acute findings, cranial nerves are intact, and the pattern is a pure peripheral neuropathy without upper motor neuron signs (no hyperreflexia, no extensor plantar responses, no spasticity). 1 MS would typically show CNS lesions and upper motor neuron findings. 2
Tick paralysis is excluded by the prolonged 4-month course and gradual progression. Tick paralysis causes acute ascending paralysis that develops over hours to days and resolves rapidly (within 24-48 hours) after tick removal. 1 The chronic progressive nature and absence of acute onset make this diagnosis untenable.
Essential Next Steps for Confirmation
Immediate diagnostic workup should include:
Electrodiagnostic studies (EMG/nerve conduction studies) to document demyelination with slowed conduction velocities, temporal dispersion, and possible conduction blocks. 2, 3 These are the most important confirmatory tests for CIDP.
Lumbar puncture for CSF analysis to look for cytoalbuminologic dissociation (elevated protein >45 mg/dL with normal cell count <10 cells/μL). 2, 3 Elevated protein strongly supports CIDP, though normal protein doesn't exclude it. 1
MRI of brachial and lumbosacral plexus to identify peripheral nerve abnormalities and rule out compressive lesions. 2, 5
Clinical Pitfalls to Avoid
Do not delay treatment pending complete diagnostic confirmation if the patient develops severe symptoms such as respiratory muscle weakness, dysphagia, or inability to ambulate. 6, 2 However, this patient can currently ambulate (though unable to walk due to weakness), so urgent treatment is not yet indicated. 6
Ensure comprehensive evaluation for secondary causes: Check for monoclonal gammopathies (serum protein electrophoresis with immunofixation), osteosclerotic myeloma (skeletal survey), HIV, hepatitis B/C, and other systemic inflammatory conditions like lupus. 3, 4, 7 CIDP can be associated with these conditions and treatment may differ.
Watch for progression: If weakness worsens to involve respiratory muscles, facial muscles, or swallowing, immediate treatment with pulse methylprednisolone 1g IV daily for 3-5 days plus IVIG 2g/kg over 5 days should be initiated. 2