What is the differential diagnosis and evaluation plan for a 13-month-old female presenting with an abnormal gait on the left side, without a history of trauma or injury, and no tenderness to palpation or range of motion (ROM) in the left lower extremity, knee, and hip?

Differential Diagnosis for Abnormal Gait in a 13-Month-Old Female

Single Most Likely Diagnosis

• Transient Synovitis: This condition is a common cause of abnormal gait in toddlers, characterized by inflammation of the synovial membrane in the hip joint. It often presents with a limp or abnormal gait without a history of trauma, which aligns with the patient's symptoms. The lack of tenderness to palpation and during range of motion (ROM) also supports this diagnosis, as transient synovitis can be relatively painless.

Other Likely Diagnoses

• Developmental Dysplasia of the Hip (DDH): Although DDH is typically diagnosed earlier in life, some cases may not be apparent until the child begins walking. The abnormal gait could be a sign of hip instability or dysplasia.
• Legg-Calve-Perthes Disease: This condition involves avascular necrosis of the femoral head and can present with a limp or abnormal gait in young children. However, it typically affects children slightly older than the patient and may be accompanied by pain.
• Infection (e.g., Osteomyelitis, Septic Arthritis): While the patient does not exhibit tenderness, infections can sometimes present subtly, especially in young children. The absence of fever or other systemic symptoms makes this less likely but still worth considering.

Do Not Miss Diagnoses

• Slipped Capital Femoral Epiphysis (SCFE): Although more common in older children and adolescents, SCFE can occur in younger children and is a critical diagnosis not to miss due to the risk of long-term hip damage. It typically presents with hip, knee, or thigh pain and a limp.
• Malignancy (e.g., Neuroblastoma, Rhabdomyosarcoma): While rare, malignancies can cause abnormal gait due to mass effect or metastasis to bones. The absence of systemic symptoms or a palpable mass makes this less likely, but it remains a critical consideration.
• Child Abuse: Non-accidental trauma must always be considered in the differential diagnosis of an unexplained limp or abnormal gait in a child, especially if there are inconsistencies in the history provided by caregivers.

Rare Diagnoses

• Juvenile Idiopathic Arthritis (JIA): This chronic autoimmune disease can cause joint inflammation and pain, leading to an abnormal gait. However, it typically presents with more systemic symptoms and involvement of multiple joints.
• Neurological Conditions (e.g., Cerebral Palsy, Muscular Dystrophy): Certain neurological conditions can cause abnormal gait patterns. However, these conditions usually have other associated symptoms and signs that would have been noted earlier in the child's development.

Overall Plan for Evaluation

1. Detailed History: Further questioning about the onset, progression, and any associated symptoms of the abnormal gait.
2. Physical Examination: A thorough examination, including observation of gait, assessment of hip and knee stability, and evaluation for any signs of neurological impairment.
3. Imaging Studies:
   • Ultrasound of the Hip: To evaluate for signs of transient synovitis or developmental dysplasia.
   • X-rays of the Hip and Lower Extremity: To assess for fractures, SCFE, or other bony abnormalities.
4. Laboratory Tests:
   • Complete Blood Count (CBC): To evaluate for signs of infection or inflammation.
   • Erythrocyte Sedimentation Rate (ESR) and C-Reactive Protein (CRP): To assess for systemic inflammation.
5. Consultations: Orthopedic consultation for further evaluation and management, especially if there's suspicion of a condition requiring surgical intervention.
6. Observation and Follow-Up: Close follow-up to monitor the resolution of symptoms or the development of new signs that might suggest a different diagnosis.