Camurati-Engelmann Disease

A Gain-of-Function in TGF-beta1

TGF-beta1 is normally secreted as a latent complex: the active cytokine bound to its latency-associated peptide (LAP). The LAP keeps TGF-beta1 inactive until it is released in a controlled way.

In CED, mutations in the LAP-coding region of TGFB1 destabilise this latent complex. The result is premature or excessive release of active TGF-beta1, increasing signalling through the TGF-beta type I receptor.

Why this matters for bone:

• TGF-beta1 is a key coupling factor between osteoblasts and osteoclasts.
• Excess active signalling drives accelerated, uncoupled bone turnover with a net gain of cortical bone along the diaphyses.
• In preclinical work, targeting the TGF-beta type I receptor reduced the high bone turnover, supporting the pathway as the central driver (Van Hul et al., Calcif Tissue Int 2019; DOI).

Osteoblasts and Osteoclasts Both Activated

Although CED produces dense bone, it is not simply a problem of absent resorption. According to PubMed, the most common mutation (R218C) actually increases TGF-beta1 bioactivity and enhances osteoclast formation and bone resorption in vitro - consistent with clinical evidence of increased bone formation AND increased bone resorption (high turnover) rather than purely dense, inert bone (McGowan et al., J Clin Endocrinol Metab 2003; DOI).

Net effect:

• Periosteal and endosteal apposition exceeds resorption at the diaphyses, producing cortical hyperostosis.
• High overall turnover explains the bone pain, raised inflammatory and bone-turnover markers, and the avid uptake on bone scan.

From Molecule to Patient

Bone pain: High-turnover periosteal new bone and periosteal stretching cause the deep, aching limb pain that is the most consistent symptom.

Proximal weakness and waddling gait: There is genuine reduced muscle mass and proximal myopathy-like weakness; the precise mechanism is incompletely understood but is linked to the systemic TGF-beta1 excess and to disuse from pain. This produces the myopathic, waddling gait.

Marfanoid / thin habitus: Many patients are tall and thin with poor muscle bulk and delayed sexual development described in some series (Nishimura et al., Am J Med Genet 2002; DOI).

Cranial nerve effects: Skull-base hyperostosis narrows neural foramina, threatening the optic, vestibulocochlear and facial nerves and occasionally raising intracranial pressure.

Classic Presentation

A child or adolescent (often thin and tall for age) presents with:

Musculoskeletal:

• Limb pain - deep, aching, in the legs and arms; the dominant complaint
• Easy fatigue and reduced exercise tolerance
• Proximal lower-limb weakness and muscle wasting
• Waddling, myopathic gait and delayed walking in younger children
• Flexion contractures of hips and knees in more severe cases

General:

• Thin, marfanoid habitus with poor muscle bulk
• Delayed puberty / delayed sexual development in some series

Cranial (skull-base involvement):

• Headaches
• Visual disturbance (optic canal narrowing)
• Hearing loss and facial palsy (less common)

A 17- and 11-year-old pair described in the literature showed marfanoid habitus, waddling gait, muscular weakness, intense leg pain, flexion contractures and raised alkaline phosphatase and ESR - illustrating the typical constellation (Nishimura et al., Am J Med Genet 2002; DOI).

Variable Expression

CED is notorious for variable expressivity, even within one family carrying the same mutation:

• Some carriers are asymptomatic and diagnosed only on family screening or incidental imaging.
• Disease may be limited to one or a few bones (for example confined to the tibia) rather than widespread.
• Atypical phenotypes have been linked to specific mutations - for example a family with disease limited to the tibia plus obesity carried a p.Arg156Cys (R156C) LAP-domain mutation, a feature not usually associated with CED (Collet et al., Am J Med Genet A 2013; DOI).

Practical point for exams: symptoms and radiographic extent do not always correlate, and a normal-looking relative may still carry the mutation.

Focused Assessment

Inspection / gait:

• Body habitus (thin, marfanoid), muscle bulk, contractures
• Observe the waddling gait; perform a sit-to-stand and Gowers-type assessment

Power:

• Proximal lower-limb power (hip flexors, abductors) - typically weak
• Compare proximal vs distal to highlight the myopathic pattern

Local bone:

• Tenderness over the diaphyses of the long bones
• Limb length and any angular deformity

Cranial nerves:

• Visual acuity and fields, fundoscopy (optic atrophy)
• Hearing, facial nerve function

Systemic:

• Look for clues of differentials (no organomegaly; CED does not cause hepatosplenomegaly, unlike severe osteopetrosis)

Radiographs - The Key Test

Plain radiographs are usually diagnostic when the pattern is recognised:

Bone scintigraphy (bone scan):

• Shows increased tracer uptake along active diaphyseal disease.
• Useful to map disease activity and distinguish active from quiescent lesions, and to guide whether painful sites are metabolically active.

CT / MRI:

• CT best shows skull-base hyperostosis and foraminal narrowing when cranial nerve symptoms are present.
• MRI helps exclude mimics (for example marrow changes of osteomyelitis or tumour) and assess soft tissues.

Blood Tests

There is no diagnostic blood test, but supportive findings include:

• Alkaline phosphatase: may be elevated (increased bone turnover)
• ESR / inflammatory markers: may be raised, reflecting active disease and contributing to the "inflammatory" feel of flares
• Calcium and phosphate: usually normal (helps exclude metabolic bone disease and rickets mimics)
• Full blood count: typically normal - no pancytopenia (an important contrast with malignant osteopetrosis)

These were illustrated by raised alkaline phosphatase and ESR in the symptomatic adolescents reported by Nishimura et al. (Am J Med Genet 2002; DOI).

Confirming the Diagnosis

• TGFB1 sequencing confirms the diagnosis in the majority of clinically typical cases. Look particularly at the LAP-domain exons where mutations cluster.
• The R218C mutation is the most common; other recurrent LAP-domain changes (for example R156C) are described.
• Independently arising, LAP-domain-specific mutations have been confirmed across multiple unrelated families, underscoring that this domain is the hotspot (Kinoshita et al., Am J Med Genet A 2004; DOI).
• A negative TGFB1 test does not exclude CED if the radiographic and clinical picture is classic - some patients are mutation-negative.
• Genetic testing supports family counselling (autosomal dominant, 50% transmission risk) and clarifies atypical or borderline cases.

First-Line Medical Therapy

Corticosteroids are the mainstay of treatment and often produce a striking response:

• Relieve bone pain, improve muscle weakness and fatigue, and can improve gait.
• May also reduce radiographic disease activity in some patients.
• Typically used at the lowest effective dose (often low-dose or alternate-day prednisone/prednisolone) to limit long-term steroid harms, especially in growing children.

According to PubMed, treatment options are currently mostly limited to corticosteroids that may relieve pain and improve muscle weakness and fatigue (Van Hul et al., Calcif Tissue Int 2019; DOI).

Targeting the TGF-beta Pathway

Because CED is driven by excess TGF-beta1 signalling, drugs that dampen this pathway are of interest.

• Losartan (an angiotensin II receptor blocker with known anti-TGF-beta activity) has been tried as a pathway-directed therapy. Responses are variable: some reports describe benefit, but according to PubMed there are also reports of failure of both conventional treatment and losartan in CED, underscoring that it is not uniformly effective (Combier et al., Joint Bone Spine 2018; DOI).
• TGF-beta type I receptor inhibition ameliorated high bone turnover in preclinical models, supporting future receptor-targeted therapy (Van Hul et al., Calcif Tissue Int 2019; DOI).
• Patient-derived iPS-cell models are being used to develop novel agents, as CED mouse models have been difficult to establish (Kinoshita, Nihon Rinsho 2015).

Symptom Control and the Surgeon's Role

Analgesia:

• NSAIDs and simple analgesics for pain; some patients use stronger analgesia during flares.

Rehabilitation:

• Physiotherapy to maintain strength, range of motion and gait, and to counter contractures and disuse weakness.
• Activity modification during painful flares.

Orthopaedic considerations:

• CED is largely a medical disease; surgery has a limited, selective role.
• Corrective osteotomy may be considered for significant limb deformity, but the dense, hyperostotic cortical bone is technically difficult to cut and fix - anticipate hard bone, prolonged drilling and a higher complication rate (the same operative caveats as other sclerosing dysplasias).
• Skull-base / cranial nerve compression is a neurosurgical problem; decompression may be considered for progressive visual or other cranial nerve loss.
• Monitor for raised intracranial pressure where skull involvement is marked.

Follow-Up

• Clinical: pain scores, muscle power, gait, growth and puberty in children.
• Cranial nerves: periodic vision and hearing assessment, especially with skull-base disease.
• Imaging: serial radiographs to track progression; bone scan to assess activity if symptoms change.
• Bloods: alkaline phosphatase / inflammatory markers can reflect activity; monitor for steroid side effects (glucose, bone density, growth).
• Genetic counselling: autosomal dominant inheritance with 50% transmission risk; offer family screening and counselling.