Differential Diagnosis: Pes Cavus with Frontal Bossing
The combination of high arches (pes cavus) and frontal bossing should immediately prompt evaluation for growth hormone excess (acromegaly/gigantism), X-linked hypophosphatemia (XLH), and hereditary peripheral neuropathies, with acromegaly being the most critical to rule out given its significant morbidity and mortality implications.
Primary Differential Diagnoses
1. Growth Hormone Excess (Acromegaly/Gigantism)
This is the most important diagnosis to exclude given its life-threatening complications.
- Frontal bossing is a classic finding of somatic enlargement from chronic GH/IGF-1 hypersecretion
- Acral enlargement (hands, feet, skull)
- Prognathism, dental malocclusion, teeth separation
- Excessive perspiration (60-80% of patients)
- Joint pain and arthropathy (up to 75% of patients)
- Soft tissue thickening, increased heel pad thickness
- Measure serum IGF-1 (age-adjusted, sex-adjusted, Tanner stage-matched)
- Oral glucose tolerance test with GH suppression (failure to suppress GH below 1 μg/L is diagnostic)
- MRI pituitary if biochemical confirmation obtained
Critical Point: In children/adolescents, look for accelerated growth velocity >+2 SDS, tall stature, or delayed puberty 1. The mortality risk in untreated acromegaly makes this the highest priority diagnosis.
2. X-Linked Hypophosphatemia (XLH)
This is the second most likely diagnosis, particularly if the patient has short stature rather than tall stature.
Key Clinical Features 3:
- Frontal bossing with dolichocephaly (parietal flattening, widened sutures)
- Pes cavus is not explicitly mentioned but lower limb deformities are prominent
- Disproportionate short stature (impaired limb growth with preserved trunk growth)
- Bowing of lower limbs (varus or valgus deformity)
- Waddling gait, delayed walking
- Dental abscesses (highly prevalent >3 years)
- Bone pain, osteomalacia in adults
Diagnostic Workup 3:
- Serum phosphate (hypophosphatemia)
- Calculate TmP/GFR (renal phosphate wasting)
- Elevated alkaline phosphatase
- Elevated intact FGF23 levels
- PHEX gene mutation analysis (70-90% detection rate)
- Radiographs: cupped/flared metaphyses, thickened cortical bone
Note: Serum phosphate may be normal in first 3-4 months of life 3.
3. Hereditary Peripheral Neuropathies
Particularly Charcot-Marie-Tooth disease (CMT), which commonly presents with pes cavus.
- Pes cavus is a cardinal and often early sign
- Bilateral foot deformities
- Hammer toes, ankle twisting
- Distal muscle hypotrophy of limbs
- Family history of pes cavus or gait impairment
- Selective denervation of intrinsic foot musculature (especially lumbricals)
Clinical Clues 5:
- Bilateral presentation
- Positive family history
- Neurological symptoms: distal weakness, sensory loss, areflexia
- Progressive gait impairment
Workup:
- Neurological examination with focus on distal strength, sensation, reflexes
- Nerve conduction studies/EMG
- Genetic testing for CMT subtypes
4. Other Considerations
Homocystinuria 6:
- Pes cavus with skeletal deformities
- Lens subluxation (superolateral)
- Genu valgum
- Pubis-heel length > crown-pubis length
- Mental retardation (variable)
- Biochemical confirmation: elevated homocysteine levels
Beckwith-Wiedemann Spectrum (BWSp) 7:
- If lateralized overgrowth is present
- Macroglossia, omphalocele, hemihypertrophy
- Frontal bossing not a primary feature
- Less likely without asymmetric overgrowth
Algorithmic Approach
Step 1: Assess stature and growth pattern
- Tall stature/accelerated growth → Prioritize acromegaly/gigantism workup
- Short stature/disproportionate → Prioritize XLH workup
Step 2: Examine for acral features
- Hand/foot enlargement, prognathism, excessive sweating → Acromegaly
- Lower limb bowing, waddling gait, dental issues → XLH
Step 3: Neurological examination
- Distal weakness, sensory loss, bilateral pes cavus → CMT/hereditary neuropathy
Step 4: Family history
- Pes cavus in relatives → Hereditary neuropathy
- Growth disorders, skeletal abnormalities → XLH or genetic syndromes
Step 5: Initial laboratory screening
- IGF-1, oral glucose tolerance test with GH
- Serum phosphate, alkaline phosphatase, TmP/GFR
- If indicated: genetic testing (PHEX, CMT panels)
Critical Pitfalls to Avoid
Do not dismiss frontal bossing as a normal variant without biochemical evaluation for GH excess—untreated acromegaly carries significant cardiovascular and metabolic mortality 2.
Do not assume idiopathic pes cavus without neurological examination—up to 75-80% of childhood scoliosis with pes cavus may have underlying neuromuscular pathology 8.
Do not miss XLH in young children—serum phosphate may be falsely normal in first 3-4 months of life; repeat testing if clinical suspicion is high 3.
Do not overlook bilateral presentation—bilateral pes cavus strongly suggests systemic/genetic etiology rather than acquired deformity 5.